Chemical engineering
Chemical engineering is the branch of engineering that deals with the application of physical science (e.g. chemistry and physics), with mathematics, to the process of converting raw materials or chemicals into more useful or valuable forms. In addition to producing useful materials, modern chemical engineering is also concerned with pioneering valuable new materials and techniques - such as nanotechnology, fuel cells and biomedical engineering.A person employed in this field is called a chemical engineer.
Chemical engineering largely involves the design and maintenance of chemical processes for large-scale manufacture. Chemical engineers in this branch are usually employed under the title of process engineer. A related term with a wider definition is chemical technology.
A
ab initio: Ab initio is Latin for "from first principles". Ab initio refers to predictions or calculations which are based entirely on theory as opposed to experimentation.
abrasive: An abrasive is a material that is used to polish surfaces or smooth rough edges. Most abrasives are very hard, brittle, and heat-resistant
absolute error: Absolute error or absolute incertainty is the uncertainty in a measurement, which is expressed using the relevant units. Also, absolute error may be used to express the inaccuracy in a measurement
absolute temperature: Absolute temperature is temperature measured using the Kelvin scale where zero is absolute zero.
absolute uncertainty: Absolute error or absolute incertainty is the uncertainty in a measurement, which is expressed using the relevant units. Also, absolute error may be used to express the inaccuracy in a measurement.
absolute zero: Absolute zero is the lowest possible state at which matter can exist, 0 K or -273.15°C.
absorbance: Absorbance is a measure of the quantity of light absorbed by a sample.
absorption: Absorption is the process by which atoms, molecules, or ions enter a bulk phase (liquid, gas, solid). Absorption differs from from adsorption, since the atoms/molecules/ions are taken up by the volume, not by surface.
absorption cross section: Absorptivity is the absorption cross section or extinction coefficient. Absorptivity varies with wavelength and is defined as the absorbance of a solution per unit path length and concentration: a = A/(bc), where a is absorptivity, A is absorbance, b is path length, and c is the concentration.
absorption spectroscopy: Absorption spectroscopy is a laboratory technique used to determine the structure and concentration of a sample based on the amount and wavelengths of light that it absorbs.
absorption spectrum: An absorption spectrum is a graph depicting the absorption of radiation by a material over a range of wavelengths.
absorptivity: see absorption cross section.
accelerator: An accelerator is a substance that speeds up (accelerates) a chemical reaction. The term often is applied to polymerization. An accelerator can speed the vulcanization of rubber or cause it to occur at a lower temperature than normal. More generally, an accelerator can speed crosslinking of polymer subunits or cause polymerization to occur at a lower temperature than normal.
accuracy: Accuracy refers to the correctness of a single measurement. Accuracy is determined by comparing the measurement against the true or accepted value.
acetate: acetate ion (CH3COO-, C2H3O2-) an ion formed by removing the acidic hydrogen from acetic acid.
acid: An acid is a chemical species that donates protons or hydrogen ions and/or accepts electrons.
Examples: Arrhenius acid, Lewis acid, hydrochloric acid.
acid anhydride: An acid anhydride is a nonmetal oxide which reacts with water to form an acidic solution.
acid-base titration: An acid-base titration is a procedure which is used to determine the concentration of an acid or base. A measured volume of an acid or base of known concentration is reacted with a sample to the equivalence point.
acid dissociation constant - Ka: The acid dissociation constant is the equilibrium constant of the dissociation reaction of an acid and is denoted by Ka.
Examples: The acid dissociation constant, Ka of the acid HB:
HB(aq) ↔ H+(aq) + B-(aq)
Ka = [H+][B-] / [HB]
acidic solution: An acidic solution is any aqueous solution which has a pH <>+] > 1.0 x 10-
actinides: Usually, the actinides are considered to be elements 90 (thorium) through 103 (lawrencium). Otherwise, the actinides are defined according to their common properties.
activated complex: An activated complex is any chemical species formed from the collision of energetic particles which is capable of reacting to form intermediates or products.
activation energy - Ea: The minimum amount of energy required to initiate a reaction and is denoted by Ea.
actual yield: The quantity of a product that is obtained from a chemical reaction (as opposed to the calculated or theoretical yield).
Adiabatic - without loss or gain of heat
addition polymer: A polymer produced through the reaction of a monomer adding to itself. No further product is formed. The monomer is most commonly a derivative of ethylene.
addition reaction: The insertion of a small molecule (e.g., H2) directly into a double or triple carbon bond.
adsorption: The adhesion of a chemical species onto the surface of particles. Adsorption is a different process from absorption, in which a substance diffuses into a liquid or solid to form a solution.
aerosol: a dispersion of a liquid in a gas or a solid in a gas.
alchemy: Several definitions of alchemy exist. Originally, alchemy was an ancient tradition of sacred chemistry used to discern the spiritual and temporal nature of reality, its structure, laws, and functions.
alcohol: substance containing an OH group attached to a hydrocarbon group.
Examples: ethyl alcohol or ethanol: C2H5OH; butyl alcohol or butanol: C4H9OH
aldehyde: an aldehyde is a substance containing the CHO group at the end of a hydrocarbon chain.
alkali metal: An alkali metal is any of the elements found in Group IA of the periodic table. Alkali metals are very reactive chemical species which readily lose their one valence electron to form ionic compounds with nonmetals.
alkaline: Alkaline refers to an aqueous solution having a pH greater than 7 or having a [OH-] greater than 10-7.Also Known As: basic.
alkaline earth metal: An alkaline earth metal is an element belonging to group 2 of the periodic table. The alkaline earth metals, as a group, share charactertic properties.
alkane: An alkane is a hydrocarbon containing only single carbon-carbon bonds.
Examples: C2H6
alkene: An alkene is a hydrocarbon containing a double carbon-carbon bond.
Examples: H2C=CH2
alkyl group: an alkyl group is a hydrocarbon group, such as CH3- or C3H7-.
alkyne: An alkyne is a hydrocarbon containing a triple carbon-carbon bond.
Example: Acetylene.
allotrope: The term allotrope refers to one or more forms of an elementary substance.
Examples: Graphite and diamond are both allotropes of carbon. O2 and ozone, O3, are allotropes of oxygen.
alloy: An alloy is a substance made by melting two or more elements together, at least one of them a metal. An alloy crystallizes upon cooling into a solid solution, mixture, or intermetallic compound.
Examples: brass, bronze, 14k gold, sterling silver.
alpha: particle He2+ ion or the helium nucleus.
amorphous: term used to describe a solid which does not exhibit crystalline structure. While there may be local ordering of the atoms or molecules in an amorphous solid, no long-term ordering is present.
Examples: window glass, polystyrene
analytical: chemistry Analytical chemistry is the chemistry discipline concerned with the chemical composition of materials. Analytical chemistry also is concerned with developing the tools used to examine chemical compositions.
anion: An ionic species having a negative charge.
androgen: androgen is the name given to any natural or synthetic compound that stimulates or controls male sex characteristics. Androgens typically are steroid hormones. Androgens are precursor molecules to estrogens, the female sex hormones.
Examples: testosterone, dihydroxytestosterone
Anisotropy: Variation of a transport property in different directions in a material. Is often obtained from homogenization of regular structures, for example, monolithic structures in tubular reactors.
antioxidant: An enzyme or other organic molecule that can counteract the damaging effects of oxygen in tissues. Although the term technically applies to molecules reacting with oxygen, it is often applied to molecules that protect from any free radical (molecules with unpaired electron).
Examples: beta-carotene, lycopene, vitamin E
Arrhenius rate equation: Expression that relates the rate constant of a chemical reaction to the exponential of the temperature
aromatic compound: An organic molecule containing a benzene ring
aqueous solution: An aqueous solution is any solution in which water (H2O) is the solvent.
Examples: cola, saltwater, rain.
astrochemistry: Astrochemistry is the chemistry of outer space. It is usually applied to regions beyond the solar system (which is sometimes termed cosmochemistry). Astrochemistry is an integration of astronomy and chemistry.
atom: The defining structure of an atom, which cannot be broken by any chemical means.
Examples: hydrogen, carbon-14, zinc, cesium, Cl- (a substance can be an atom and an isotope or ion at the same time)
atomic mass: Atomic mass or atomic weight is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element.
Also Known As: Atomic Weight
Examples: The atomic mass of carbon is 12.011; the atomic mass of hydrogen is 1.0079
atomic mass unit (amu): an atomic mass unit or amu is one twelfth of the mass of an unbound atom of carbon-12. It is a unit of mass used to express atomic masses and molecular masses.
Also Known As: unified atomic mass unit (u), Dalton (Da) or universal mass unit
atomic number: The number of protons in an element.
Examples: The atomic number of hydrogen is 1; the atomic number of carbon is 6.
atomic radius: The atomic radius is a term used to describe the size of the atom, but there is no standard definition for this value. Atomic radius may refer to the ionic radius, covalent radius, metallic radius, or van der Waals radius. In all cases, the size of the atom is dependent on how far out the electrons extend. The atomic radius for an element tends to increase as one goes down an element group. The electrons become more tightly packed as you move across the periodic table, so while there are more electrons for elements of increasing atomic number, the atomic radius actually may decrease.
atomic weight: The average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. It is the weighted average of the masses of naturally-occurring isotopes.
Also Known As: Atomic Mass
Examples: The atomic mass of carbon is 12.011; the atomic mass of hydrogen is 1.0079
Avogadro's number: Avogadro's number is the number of particles found in one mole of a substance. It is the number of atoms in exactly
Also Known As: Avogadro's constant
Azeotrope: a specific mixture of components, which at a given pressure cannot be separated by distillation, i.e. the liquid and vapour phases have the same compositions.
B
Baeyer reagent: Dilute cold potassium permanganate solution, used to oxidize alkenes and alkynes.
balanced equation: An equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge are the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction.
Balmer series: The portion of the emission spectrum of hydrogen that represents electron transitions from energy levels n > 2 to n = 2. These are four lines in the visible spectrum.
Examples: The four visible Balmer lines of hydrogen appear at 410 nm, 434 nm, 486 nm and 656 nm.
base A: base is a chemical species that donates electrons or hydroxide ions or that accepts protons.
Types of Bases: Arrhenius base, Bronsted-Lowry base, Lewis base. nitrogen base.
base dissociation constant (Kb): Equilibrium constant that measures the extent of dissociation for a base.
Example: The Base Dissociation Constant (Kb) for a base BOH is denoted by:
Kb = [B+]·[OH-] / [BOH]
basic: An aqueous solution containing more OH- ions than H+ ions. An aqueous solution with a pH greater than 7.
basic solution: An aqueous solution containing more OH- ions than H+ ions. An aqueous solution with a pH greater than 7.
batch reactor: Reactor characterized by its operation, which means that the reactor does reaches steady state.
benzenoid ring: an aromatic ring that possesses a benzene-like structure.
benzyl group: The C6H5CH2 group. An organic chemical group.
benzyne: In organic chemistry: an unstable intermediate species consisting of a benzene ring with an adjacent chemical bond created by the side-to-side overlap of the sp2 orbitals on the adjacent carbon atoms of the ring.
beta particle: An electron or positron. The term is generally applied to an electron or positron emitted in radioactive beta decay.
binding energy: The energy required to either separate an electron from an atom or to separate the protons and neutrons of an atomic nucleus.
biochemistry: Biochemistry is the chemistry of living things. It is concerned with the structure and chemical processes of proteins, carbohydrates, lipids, nucleic acids and other molecules found in or produced by organisms.
biology: the scientific study of life. Biology involves the study of living organisms and how they relate to their environment. Fields of biology include botany, zoology, microbiology, biochemistry, genetics, molecular biology, cellular biology, physiology, and ecology.
bipolar plate: Electrically conducting plate connected to the anode on one side and to the cathode on the other side in an electrochemical cell.
black light: a black light is a lamp that emits electromagnetic radiation primarily in the soft near ultraviolet range. A black light emits very little visible light, hence its name.
boiling: a phase transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point.
Also Known As: ebullition
Example: boiling is seen when water is heated until it forms steam
boiling point: the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid. Therefore, the boiling point of a liquid depends on atmospheric pressure. The boiling point becomes lower as the external pressure is reduced.
boiling point elevation: the phenomenon that occurs when the boiling point of a liquid (a solvent) is increased when another compound is added, such that the solution has a higher boiling point than the pure solvent. Boiling point elevation occurs whenever a non-volatile solute is added to a pure solvent.
Example: The boiling point of salted water is higher than the boiling point of pure water.
bond: a link between atoms in molecules and between ions and molecules in crystals. Examples: covalent bonds, ionic bonds
bond angle: The angle that is formed between two adjacent bonds on the same atom.
bond-dissociation energy: the amount of energy which is required to homolytically fracture a chemical bond.
bond length: the equilibrium distance between the nuclei of two groups or atoms that are bonded to each other.
bonding molecular orbital: The orbital which is formed by the overlap of adjacent atomic orbitals.
boundary layer: Region in a fluid close to a solid surface. This region is characterized by large gradients in velocity and is often treated with approximative methods, because it is difficult to geometrically resolve the large gradients found there.
branched chain alkane: An alkane which has alkyl groups bonded to its central carbon chain.
brass: An alloy of copper and zinc.
Brinkman equations: Extension of Darcy’s law in order to include the transport of momentum through shear in porous media flow.
Bronsted-Lowry acid: a Bronsted-Lowry acid is a material that gives up hydrogen ions during a chemical reaction.
Bronsted-Lowry base: a Bronsted-Lowry base is a material that accepts hydrogen ions during a chemical reaction.
bronze: An alloy of copper, usually containing tin as its main addition.
buffer: A solution containing either a weak acid and its salt or a weak base and its salt, which is resistant to changes in pH.
Examples: blood.
Butler-Volmer equation: Expression that relates the reaction rate of an electron transfer reaction on an electrode surface to the exponential of the overpotential. The equation can be derived from the Arrhenius rate equation by accounting for the contribution of the electric potential to the activation energy.
Bubble Point: upon heating a liquid mixture, this is the point at which bubbles first appear.
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Calibration: Process of determining the relation between the output or response of a measuring instrument and the value of the input. Calibration typically involves the use of a measuring standard.
calomel: This is a common name for mercury chloride, Hg2Cl2.
calorie: A unit of thermal energy equal to 4.184 joules or the amount of energy required to raise the temperature of
calorimeter: A device used to measure the heat flow of a chemical reaction or physical change.
calorimeter constant (C): Denoted by 'C'. This is the product of the mass multiplied by the specific heat of a bomb calorimeter.
carbanion: a carbon atom which has a negative electrical charge. A carbon anion.
carbohydrate: A class of organic compounds having the general formula Cm(H2O)n.
Examples: Glucose, fructose, sucrose, starch, cellulose.
carbonate ion: The chemical species CO32-
carbonyl: the term carbonyl refers to the carbonyl functional group which is a divalent group consisting of a carbon atom with a double-bond to oxygen. Carbonyl also may refer to a compound formed by a metal with carbon monoxide.
Example: An example is acetic acid, CH3COOH
carboxylic acid: An organic compound containing the COOH functional group.
carotenoid: A family of natural pigments found in plants and animals. Plants are the source of the carotenoids found in animals.
catalyst: A subtance that increases the rate of a chemical reaction by reducing the activation energy, but which is left unchanged by the reaction.
Examples: A piece of platinum foil is a catalyst for the combustion of methane in air.
cathode: a cathode is the electrode at which reduction occurs.
cathode ray tube: A cathode ray tube is a type of vacuum tube which contains a source of electrons and a fluorescent screen, with some means to accelerate and deflect the electron beam. Cathode ray tubes commonly are used to form images on the fluorescent screen.
Also Known As: CRT
cation ionic: species with a positive charge.
Examples: Ca2+, Li+
Celsius temperature scale: The Celsius temperature scale is a common but non-SI temperature scale which is defined by assigning the temperatures of
chalcogen: name given to a member of periodic table group 16 (old-style: VIB or VIA) in the periodic table. Chalcogens are sometimes known as the oxygen family. The chalcogens are the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and ununhexium (Uuh). The compounds of the heavier chalcogens (the sulfides, selenides, and tellurides) are known as chalcogenides.
charge: In the context of chemistry, charge usually refers to electric charge, which is a conserved property of certain subatomic particles that determines their electromagnetic interaction.
chemical: Everything which has mass is a chemical. Anything consisting of matter is a chemical. Any liquid, solid, gas. Any pure substance; any mixture.
Examples: water, pencil, air, carpet, lightbulb, copper, bubbles, baking soda
chemical physics: Physical chemistry is the branch of chemistry that is concerned with the application of physics to chemical systems. This may involve the application of the principles of thermodynamics, quantum mechanics, quantum chemistry, statistical mechanics and kinetics to the study of chemistry.
chemisorption: See adsorption.
chemistry: The scientific study of matter, its properties, and interactions with other matter and with energy.
chiral center: A chiral center is defined as an atom in a molecule that is bonded to four different chemical species, allowing for optical isomerism.
Examples: The central carbon in serine is a chiral carbon. The amino group and hydrogen can rotate about the carbon.
chloride: A chloride is any chemical compound in which one or more chlorine atoms are covalently bonded within the molecule. The term chloride may refer to any salt of hydrochloric acid, HCl, which contains chloride ions. Chloride ions form when the element chlorine picks up an electron to form an anion Cl−.
colligative: properties properties of solutions that depend on the number of particles in a volume of solvent and not on the mass of the particles.
colloid crystallization: is the slow precipitation of crystals from a solution of a substance. Crystallization can also refer to the solid-liquid separation and purification technique in which mass transfer occurs from the liquid solution to a pure solid crystalline phase.
combustion: Combustion is a chemical reaction chemical that occurs between a fuel and an oxidizing agent that produces energy, usually in the form of heat and light.
compound: species that is formed when two or more atoms join together chemically, with covalent or ionic bonds.
Also Known As: molecule, though sometimes distinctions are made between the types of bonds in molecules (covalent) and compounds (ionic)
concentrated: Concentrated refers to a relatively large quantity of substance present in a unit amount of mixture.
concentration: The amount of a substance per defined space. Concentration usually is expressed in terms of mass per unit volume.
Examples: g/cm3, kg/l
condensation: change in the state of matter from the gas phase to the liquid phase.
conductor: A conductor is a material which permits a flow of energy. A material which allows the flow of charged particles is an electrical conductor. A material which allows the transfer of thermal energy is a thermal conductor or heat conductor.
conjugate: In chemistry, a conjugate refers to a compound formed by the joining of two or more chemical compounds or the term conjugate refers to an acid and base that differ from each other by a proton.
conjugate acid: A conjugate acid is the acid member, HX, of a pair of compounds that differ from each other by gain or loss of a proton. A conjugate acid can release or donate a proton.
conjugate base: A conjugate base is the base member, X-, of a pair of compounds that transform into each other by gaining or losing a proton. The conjugate base gains or absorbs a proton in a chemical reaction.
conservation of energy: Law which states energy cannot be created or destroyed, but may be changed from one form to another.
conservation of mass: Law of Conservation of Mass is a relation stating that in a chemical reaction, the mass of the products equals the mass of the reactants.
continuous reactor: Reactor that operates without interruption. This type of reactor is characterized by its steady-state operation.
coordination compound: a compound containing one or more coordinate bonds, which is a link between a pair of electrons in which both electrons are donated by one of the atoms.
Examples: most metal complexes or compounds except for alloys. Specific examples include hemoglobin and Ru3(CO)12
covalent bond: A chemical link between two atoms in which electrons are shared between them.
Examples: There is a covalent bond between the oxygen and each hydrogen in a water molecule (H2O). Each of the covalent bonds contains two electrons - one from a hydrogen atom and one from the oxygen atom. Both atoms share the electrons.
covalent compound: a molecule formed by covalent bonds, in which the atoms share one or more pairs of valence electrons
covalent radius: The covalent radius refers to the size of atom that forms part of a covalent bond. Covalent radius is expressed in terms of picometers or angstroms. In theory, the sum of two covalent radii should equal the covalent bond length between two atoms, but in practice the length of the bond depends on the chemical environment.
critical point: The critical point or critical state is the point at which two phases of a substance initially become indistinguishable from one another.
Crystal: a substance in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating three-dimensional pattern. Most crystals are solids. Examples: quartz, rock candy, halite
Crystallize: crystallization is the slow precipitation of crystals from a solution of a substance. Crystallization can also refer to the solid-liquid separation and purification technique in which mass transfer occurs from the liquid solution to a pure solid crystalline phase.
CSTR: Continuous Stirred Tank Reactor. This may be thought of as a tank to which reactants flow in, and products flow out. In an ideal CSTR the contents of the reactor are uniformly distributed.
D
Dalton's Law: A relation which states the total pressure of a mixture of gases is equal to the sum of the partial pressures of its component gases.
Darcy’s law: Equation that gives the velocity vector as proportional to the pressure gradient. Often used to describe flow in porous media.
Data: Any representation to which meaning can be attached.
Also Known As: information
Examples: characters, numbers, words.
Daughter Isotope: The product which remains after an original isotope has undergone radioactive decay. The original isotope is termed the 'parent'.
de Broglie Equation: an equation used to describe the wave properties of matter, specifically, the wave nature of the electron: λ = h/mv,where λ is wavelength, h is Planck's constant, m is the mass of a particle, moving at a velocity v.
decadic absorbance: Absorbance is a measure of the quantity of light absorbed by a sample.
Also Known As: Optical Density, Extinction, Decadic Absorbance
decay constant: This is the proportionality constant between the rate of radioactive nuclear decay and the number of radioactive nuclei remaining.
deionization: The removal of ions. The term is generally used with respect to removal of ions from water. Deionization is commonly achieved by passing the water through successive ion exchange columns. In one column, ions are exchanged for H+ ions. In another column, anions are exchanged for OH- ions. Following a reaction of H+ with OH- ions, no ions remain in solution.
deliquescence: the process in which a soluble substance picks up water vapor from the air to fom a solution. In order for deliquescence to occur, the vapor pressure of the water in the air must be greater than the vapor pressure of the saturated solution.
density: Mass per unit volume.
Example: The density of pure water is defined to be
desiccant: A desiccant is a drying agent. A chemical species which picks up water molecules.
detergent: a cleaning agent. A detergent is similar to a soap, but with a general structure R-SO4-, Na+, where R is a long-chain alkyl group.
deposition: the settling of particles or sediment onto a surface. The particles may originate from a vapor, solution, suspension, or mixture.
deuterium: One of the heavy isotopes of hydrogen, with two neutrons: 12H.
Dew Point: upon cooling a vapour mixture, this is the point at which droplets of liquid first appear.
diamagnetic: Descriptive term which indicates that a substance contains no unpaired electrons and thus is not attracted to a magnetic field.
Examples: NH3 is diamagnetic because all of the electrons in NH3 are paired.
diffusion: Movement of a fluid from an area of higher concentration to an area of lower concentration. Diffusion is a result of the kinetic properties of particles of matter. The particles will mix until they are evenly distributed.
Example: H2S(g) in a test tube will slowly diffuse into the air of a lab until equilibrium is reached.
diffusion layer: Fictitious layer in a fluid close to a solid surface where a chemical reaction takes place. The flux of species perpendicular to the surface in this layer is dominated by diffusion.
dilute: a solution containing a relatively small quantity of solute as compared with the amount of solvent. This term is the opposite of 'concentrated'.
dissolve: to cause a solute to pass into solution.
DNA: Acronym for deoxyribonucleic acid, usually 2'-deoxy-5'-ribonucleic acid. DNA is a code used within cells to form proteins.
E
ebullition: a phase transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point.
Also Known As: boiling
Example: boiling is seen when water is heated until it forms steam.
effervescence: Foaming formed as a result of a gas being evolved from a solid or liquid.
efflorescence: The process of losing water of hydration from a hydrate.
effusion: the movement of a gas through a pore or capillary into another gaseous region or into a vacuum.
Einstein's equation: the relation ΔE = Δmc2, relating energy and mass changes, where E is energy, m is mass, and c is the speed of light.
electrochemistry: Electrochemistry is the scientific study of the chemical species and reactions that take place at the interface between an electron conductor and an ion conductor (electrolyte) in which an electron transfer occurs between the electrode and the electrolyte in solution.
electrode: The term is general and can be applied to either the anode or cathode side of an electrical cell.
electrolysis: electrolysis is the passage of a direct electric current through an ion-containing solution. Electrolysis produces chemical changes at the electrodes.
electrolyte: A substance which forms ions in an aqueous solution.
Examples: NaCl forms Na+ and Cl- in water.
electrolytic: cell a type of chemical cell in which the flow of electric energy from an external source causes a redox reaction to occur.
electron: a negatively charged component of an atom. Electrons exist outside of and surrounding the atom nucleus. Each electron carries one unit of negative charge and has a very small mass as compared with that of a neutron or proton.
electron affinity: Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity.
Example: The electron affinity of hydrogen is ΔH in the reaction
H(g) + e- → H-(g); ΔH = -73 kJ/mol.
electron cloud: The region of negative charge surrounding an atomic nucleus that is associated with an atomic orbital.
electron configuration: A statement describing the populations of electronic energy sublevels of an atom. See the chart of electronic configurations to get the notation for all of the elements.
Examples: The electronic configuration of the lithium atom is 1s22s, which indicates there are two electrons in the 1s sublevel and one electron in the 2s energy sublevel.
electron pair: a pair of electrons in one orbital which have opposite spins or a pair of electrons in a covalent or coordinate bond.
electron pair repulsion: the principle that electron pairs around a central atom tend to orient themselves as far apart as possible. Electron pair repulsion is used to predict the geometry of a molecule or a polyatomic ion.
electron-sea model: a model of metallic bonding in which cations are considered to be fixed points within a mobile 'sea' of electrons.
electron spin: A property of an electron that is loosely related to its spin about an axis. Two electron spin states are allowed, which are described by the quantum number ms, with values of +½ or -½.
electronegativity: A property of an atom which increases with its tendency to attract the electrons of a bond.
Examples: The chlorine atom has a higher electronegativity than the hydrogen atom, so the bonding electrons will be closer to the Cl than to the H in the HCl molecule.
electroneutrality condition: Condition that states that the sum of charges in a control volume in an electrolyte should be zero.
electroosmosis: Onset of a flow due to the application of an external electric field or due to the formation of an electric field created by ion transport in membranes, for example.
electrophoresis: Migration of charged electrolyte ions in an electric field.
electrostatic forces: the forces between particles that are caused by their electric charges.
element: A substance that cannot be broken down by chemical means. Elements are defined by the number of protons they possess.
Examples: copper, cesium, iron, neon
element symbol: usually refers to the one- or two-letter abbreviation for a chemical element, though the term can be applied to the alchemical symbols also.Examples: H for hydrogen, He for helium, Ca for calcium.
enantiomer: One of a pair of optical isomers.
Examples: The central carbon in serine is the chiral carbon. The amino group and hydrogen can rotate about the carbon, resulting in two enantiomers of serine, L-serine and D-serine.
endothermic: "within heating" from the Greek prefix endo-, meaning “inside” and the Greek suffix –thermic, meaning “to heat”. The term "endothermic" describes a process which absorbs thermal (heat) energy.
Example: Depressuring a pressurized can is an example of an endothermic process.
energy: Energy may be defined as the ability to do work. It is a scalar physical quantity. Although energy is conserved, there are many different types of energy, such as kinetic energy, potential energy, light, sound, and nuclear energy.
engineering: Engineering is the application of scientific principles to design or develop structures, equipment, or processes. The main branches of engineering include electrical engineering, mechanical engineering, chemical engineering, civil engineering, aerospace engineering, automotive engineering, and computer engineering. A person who practices engineering is called an engineer.
entropy: The measure of the disorder of a system, usually denoted by the letter S. A highly ordered system has low entropy.
Example: A block of ice will increase in entropy as it melts.
Euler flow: Flow at high velocities, where incompressibility of the fluid is of importance whereas the influence of viscous momentum transport is negligible.
evaporation: the process by which molecules undergo the a spontaneous transition from the liquid phase to the gas phase. Evaporation is the opposite of condensation.
Example: The gradual drying of damp clothes is caused by the evaporation of water into water vapor.
exothermic: term used to describe a reaction or process that releases energy in the form of heat. Sometimes the term is applied to processes that release other forms of energy, such as electrical energy, sound, or light.
Example: combustion of wood
exothermic reaction: A chemical reaction that produces heat (has a negative ΔH).
extinction: Absorbance
extinction coefficient: Absorptivity
F
f subshell: A subshell that corresponds to the angular momentum quantum number l = 3, found in the fourth and higher principal energy levels. Each contains seven orbitals.
face-centered cubic: A crystal unit cell that is cubic in shape with identical atoms at each corner and in the center of each face.
Example: Calcium and strontium form this type of unit cell, as do many of the transition elements.
Faraday (F): A unit of charge denoted by F equal to the total charge on 1 mole of electrons.
fat: Compounds that are generally soluble in organic solvents and largely insoluble in water. Fats are triesters of glycerol and fatty acids. Fats may be either solid or liquid, though sometimes the term is reserved for solid compounds.
Examples: butter, cream, lard, vegetable oil
first law of thermodynamics: The law which states that the total energy of a system and its surroundings remains constant.
Alternate Definition: The change in the energy of a system equals the heat flow in the system from the surroundings minus the work done by the system on the surroundings. Also known as the Law of Conservation of Energy.
fission: Splitting of an atomic nucleus into two or more lighter nuclei and energy is released. The original heavy atom is termed the parent nucleus and the lighter nuclei are daughter nuclei.
fluid: a fluid is any substance that flows or deforms under an applied shear stress. Fluids comprise a subset of the states of matter and include liquids, gases, and plasma. Examples: all liquids and gases are fluids (air, water, oil)
fractional distillation: A process by which components in a chemical mixture are separated according to their different boiling points. Vapors from a boiling solution are passed along a column. The temperature of the column gradually decreases along its length. Components with a higher boiling points condense on the column and return to the solution; components with a lower boiling points pass through the column and are collected.
Examples: Gasoline is produced from crude oil using fractional distillation.
fluorescence: fluorescence is luminescence that occurs where the energy is supplied by electromagnetic radiation, usually ultraviolet light. The energy source kicks an electron of an atom from a lower energy state into an "excited" higher energy state; then the electron releases the energy in the form of light (luminescence) when it falls back to a lower energy state.
Examples: fluorescent lights, the red glow of rubies in sunlight
free radical: A molecule with an unpaired electron. Because they have a free electron, such molecules are highly reactive.
Examples: singlet oxygen, free hydroxy group.
freezing: the process through which a substance changes from a liquid to a solid. All liquids except helium undergo freezing when the temperature becomes sufficiently cold.Example: water changing to ice.
freezing point: the temperature at which a liquid changes to a solid. The freezing point of a substance is not necessarily the same as its melting point.
freezing point depression: the phenomenon that occurs when the freezing point of a liquid (a solvent) is lowered by adding another compound to it, such that the solution has a lower freezing point than the pure solvent.
Example: The freezing point of seawater or even ordinary saltwater is lower than the freezing point of pure water.
fully developed laminar flow: Laminar flow along a channel or pipe that only has velocity components in the main direction of the flow. The velocity profile perpendicular to the flow does not change downstream in the flow.
functional groups: specific group of atoms within a molecule that is responsible for characteristic chemical reactions of that molecule.
Also Known As: Functional Moiety Examples: alcohol -OH, aldehyde –COH
fusion Combining lighter atomic nuclei to form a heavier nucleus. Energy is released.
G
Galvanized Steel: Steel that has been covered with a layer of zinc metal.
gamma radiation High: energy photons that are emitted by radioactive nuclei. Gamma radiation is very high-energy ionizing radiation. Gamma rays originate in the nucleus, while X-rays originate in the electron cloud around the nucleus.
gas state of matter: consisting of particles that have neither a defined volume nor defined shape.
Examples: air, chlorine at room temperature and pressure, ozone.
gas constant (R): The constant in the equation for the Ideal Gas Law:
PV = nRT
Geiger-Müller counter: A device used to measure the rate of radioactive decay. A type of radiation detector.
geochemistry: Geochemistry is the scientific study of the chemical composition of the Earth and other planets. It includes analysis of the chemical composition and reactions involving rocks, minerals and soils; the cycles of matter and energy in the earth, water, and air; and the ongoing processes that formed the Earth and change it.
geology: geology is the scientific study of the earth and the matter of which it is made. It includes the study of volcanoes, rocks, minerals, gemstones, earthquakes, fossil fuels, metals, and tectonics. Geologists seek to understand how the earth was formed, the processes that affect it, its properties, and its structure.
geometric isomer: A chemical species with the same type and quantity of atoms as another species, yet having a different geometric structure.
Examples: Two geometric isomers exist for Pt(NH3)2Cl2, one in which the species are arranged around the Pt in the order Cl, Cl, NH3, NH3, and another in which the species are ordered NH3, Cl, NH3, Cl.
Gibbs-Helmholtz equation: A relationship between ΔG, ΔH, and ΔS: ΔG = ΔH - TΔS, where T is temperature, H is enthalpy, S is entropy, and G is free energy.
glass: an amorphous solid. The term is usually applied to inorganic solids and not to plastics or other organics. Glasses do not have crystalline internal structure. They usually are hard and brittle solids.
Examples: borosilicate glass, soda-lime glass, isinglass
glass transition temperature: temperature at which an amorphous solid becomes soft upon heating or brittle upon cooling.
Graham's Law: A relation which states that the rate of the effusion of a gas is inversely proportional to the square root of its density or molecular mass.
gram: A unit of mass in the metric system equal to the mass of one cubic centimeter of water at
gram molecular mass: The mass in grams of one mole of a molecular substance.
Examples: The molecular mass of N2 is 28, so the gram molecular mass of N2 is
gray: A unit of the absorbed dose of radiation. One gray is one joule per kilogram of tissue.
greenhouse effect: The effect of water and carbon dioxide absorbing outgoing infrared radiation, raising a system's temperature. The term is generally used with reference to the Earth's temperature, although it can also be applied to other systems, such as greenhouses and automobiles.
ground state: The lowest allowed energy state of an atom, molecule, or ion.
group: A vertical column in the Periodic Table.
For further information, read about the Chemistry of Groups.
Groups I, II, III, IV: Cation groups in qualitative analysis. Roman numeral distinguish groups in the Periodic Table. For further information, read about the Chemistry of Groups and the Introduction to Qualitative Analysis.
H
Haber process: an industrial process that is used to make ammonia from hydrogen and nitrogen.
Hagen-Poiseuille equation: See Poiseuille’s law.
half-cell: A half-cell is half of an electrolytic or voltaic cell, where either oxidation or reduction occurs. The half-cell reaction at the anode is oxidation, while the half-cell reaction at the cathode is reduction.
half-equation: An equation written to describe an oxidation or reduction half-reaction.
Examples: Zn (s) → Zn2+ (aq) + 2e- is an example of an oxidation half-equation.
half-life (t1/2): The time required to convert one half of a reactant to product. The term is commonly applied to radioactive decay, where the reactant is the parent isotope and the product is a daughter isotope.
half-reaction: either the reduction reaction or the oxidation reaction of a complete redox reaction. The half reactions each occur at an electrode of an electrochemical cell.
halide ion: A singlet halogen atom, which is an anion with a charge of -1.
Examples: F-, Cl-, Br-, I-
halogen: A element located in Group VIIA of the periodic table. Halogens are reactive nonmetals having seven valence electrons.
Examples: fluorine, chlorine, bromine, iodine.
hard water: Water that contains high amounts of Ca2+ and/or Mg2+.
heat: Heat is the form of energy that flows between two samples of matter due to their difference in temperature. Usually denoted by the variable 'Q'.
heat of formation ( ΔHf): the heat released or absorbed (enthalpy change) during the formation of a pure substance from its elements, at constant pressure and usually denoted by ΔHf.
heat of fusion ( ΔHfus): The change in enthalpy for the conversion of 1 mole or
heat of sublimation ( ΔHsub): The change in enthalpy for the conversion of 1 mole or
heat of vaporization ( ΔHvap): The change in enthalpy for the conversion of 1 mole or
Heisenberg uncertainty principle: The scientific principle stating that it is impossible to determine with perfect accuracy both the position and momentum of a particle at any given point in time.
Henderson-Hasselbalch equation: an approximate equation that shows the relationship between the pH or pOH of a solution and the pKa or pKb and the ratio of the concentrations of the dissociated chemical species.
Examples: pH = pKa + log ([conjugate base]/[weak acid]) or pOH = pKa + log ([conjugate acid]/[weak base])
Henry's Law: Chemistry law which states that the mass of a gas which will dissolve into a solution is directly proportional to the partial pressure of that gas above the solution.
Hess's Law: Law which states that the energy change in an overall chemical reaction is equal to the sum of the energy changes in the individual reactions comprising it.
Heterogeneous: containing more than one phase.
heterogeneous reaction: Reaction that takes place at the interface between two phases.
Homogeneous: containing a single phase.
homogeneous reaction: Reaction that takes place in the bulk of a solution.
hormone: a hormone is a molecule that is secreted directly into the bloodstream of an organism through a ductless gland. The molecule acts as a chemical messenger, carrying information from one cell or group of cells to another area.
Examples: epinephrine, melatonin, serotonin, insulin, testosterone.
hydrocarbon: A hydrocarbon is a substance consisting only of carbon and hydrogen atoms.
Examples: benzene, hexane
hydrogen bond: A type of attractive (dipole-dipole) interaction between an electronegative atom and a hydrogen atom bonded to another electronegative atom. This bond always involves a hydrogen atom. Hydrogen bonds can occur between molecules or within parts of a single molecule. A hydrogen bond tends to be stronger than van der Waals forces, but weaker than covalent bonds or ionic bonds.
hydrogenation: Hydrogenation is a reduction reaction which results in an addition of hydrogen (usually as H2). If an organic compound is hydrogenated, it becomes more 'saturated'. Hydrogenation has many applications, but most people are familiar with the reaction as the one used to make liquid oils into semi-solid and solid fats. There may be some health concerns associated with hydrogenation of unsaturated dietary fats to produce saturated fats and trans fats.
hydronium ion: name given to the H3O+ cation, derived from the protonation of water. The hydronium ion is the simplest type of oxonium ion.
I
ideal gas: gas whose pressure P, volume V, and temperature T are related by the ideal gas law PV = nRT,where n is the number of moles of the gas and R is the ideal gas constant. Ideal gases are defined as having molecules with negligible size with an average molar kinetic energy dependent only on temperature. At low temperature, most gases behave enough like ideal gases that the ideal gas law can be applied to them.
ideal gas constant: The constant in the equation for the Ideal Gas Law: PV = nRT, where P is pressure, V is volume, n is number of moles, and T is temperature. The gas constant 'R' equals 0.0821 liter·atm/mol·K
Immiscible: Two liquids are said to be immiscible, if when added together they do not mix but form two separate liquid phases.
incandescence: The release of light by a body due to its temperature. The light usually is in the infrared and visible regions of the electromagnetic spectrum.
Examples: glow of molten lava, red-hot frying pan, glow of the filament in a light bulb
ion: an atom or molecule which has gained or lost one or more of its valence electrons, giving it a net positive or negative electrical charge.
Examples: alpha particle He2+, hydroxide OH-
ionic: pertaining to something carrying a net electrical charge, as an ionic bond or ionic compound.
ionic bond: A chemical link between two atoms caused by the electrostatic force between oppositely-charged ions in an ionic compound.
Examples: There is an ionic bond between the sodium and chloride ions in table salt, NaCl.
ionization energy: Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first or initial ionization energy or Ei of an atom or molecule is the energy required to remove one mole of electrons from one mole of isolated gaseous atoms or ions. You may think of ionization energy as a measure of the difficulty of removing electron or the strength by which an electron is bound. The higher the ionization energy, the more difficult it is to remove an electron. Therefore, ionization energy is in indicator of reactivity.
ionization potential: look ionización energy:
insoluble: incapable of dissolving in a solvent. It is rare for absolutely no solute to dissolve at all.
isomer: A chemical species with the same number and types of atoms as another chemical species, but possessing different properties. There are structural isomers, geometric isomers, optical isomers, and stereoisomers.
Examples: Pentane, 2-methylbutane, and 2,2-dimethylpropane are structural isomers of each other.
isomerization process: In the production of gasoline, a process by which straight chain hydrocarbons are converted into branched chain hydrocarbons.
Examples: Isomerization of pentane to 2-methylbutane and 2,2-dimethylpropane.
isotopes: Atoms with the same number of protons, but differing numbers of neutrons. Isotopes are different forms of a single element.
Examples: Carbon 12 and Carbon 14 are both isotopes of carbon, one with 6 neutrons and one with 8 neutrons (both with 6 protons).
J
joule: The basic SI unit of energy. A joule is equal to the kinetic energy of a kilogram mass moving at the speed of one meter per second.
K
Kelvin temperature scale: An absolute temperature scale based on the definition that the volume of a gas at constant (low) pressure is directly proportional to temperature and that 100 degrees separates the freezing and boiling points of water.
Usage: Kelvin temperatures are written with a capital letter 'K' and without the degree symbol, such as 1 K, 1120 K. Note that 0 K is 'absolute zero' and there are no negative Kelvin temperatures.
ketone: An organic compound containing a nonterminal carbonyl, C=O group.
Examples: The simplest ketone is acetone, CH3-CO-CH3
kilo: A prefix used on metric units to indicate a multiple of 1000.
Example:
kilogram (kg): The basic SI unit of mass.
kilopascal (kPa): A unit of pressure. 1 kPa is approximately the pressure exerted by a 10-g mass resting on a 1-cm2 area. 101.3 kPa = 1 atm. There are 1,000 pascals in 1 kilopascal.
kinetic: A term associated with motion.
Example of Usage: The kinetic energy of a particle is equal to ½ multiplied by its mass multiplied by the square of its velocity.
kinetic energy: Kinetic energy is the energy an object possesses due to its motion. An object of mass m moving at velocity v has a kinetic energy equal to ½mv2.
kinetic theory: A model of molecular motion that is used to explain many of the properties of gases.
kinetics:The study of the rates of chemical reactions.
L
law of the wall: See wall function.
labile complex: A complex ion which quickly reaches equilibrium with the ligands in a surrounding solution.
lanthanides: Elements with atomic numbers 58-71 (although there is some dispute over exactly where the lanthanides begin and end!). The lanthanide series is the group of elements in which the
Also Known As: Rare earth metals, rare earth elements, common earth elements.
lattice energy ΔH: (enthalpy change) for the process in which oppositely charged ions in the gas phase combine to form an ionic lattice in the solid phase.
Law of Chemical Equilibrium: A relation stating that in a reaction mixture at equilibrium, there is a condition (given by the equilibrium constant, Kc) relating the concentrations of the reactants and products. For the reaction
aA(g) + bB(g) ↔ cC(g) + dD(g), Kc = [ C ]c·[ D ]d / [ A ]a·[ B ]b
Law of Combining Volumes: A relation stating that the relative volumes of gases in a chemical reaction are present in the ratio of small integers (assuming all gases are at the same temperature and pressure).
Also Known As: Gay-Lussac's Law
Examples: In the reaction
2 H2(g) + O2(g) → 2 H2O(g)
2 volumes of H2 react with 1 volume of O2 to produce 2 volumes of H2O.
Law of Constant Composition: Law which states samples of a pure compound always contain the same elements in the same mass proportion.
Also Known As: Law of Definite Proportions
Law of Multiple Proportions: Law which states that when elements combine, they do so in the ratio of small whole numbers (assuming they have the same type of chemical bonds).
Also Known As: Dalton's Law, though that term usually refers to his law of partial pressure
Examples: carbon and oxygen react to form CO or CO2, but not CO1.6
ligand: an atom, ion, or molecule that donates or shares one or more of its electrons through a covalent bond with a central atom or ion. It is a complexing group in coordination chemistry that stabilizes the central atom and determines it reactivity.
lipid: Any fat-soluble naturally-occurring molecule.
Examples: fats, oils, waxes, sterols
Cholesterol is a lipid that is found in the cell membranes of all animal cells. It also is a sterol, which is a steroid characterized by an alcohol group.
liquid: a liquid is one of the states of matter. The particles in a liquid are free to flow, so while a liquid has a definite volume, it does not have a definite shape.
Mercury is a heavy silvery metal that is liquid at room temperature.
Examples: at room temperature: water, mercury, vegetable oil, [/link]ethanol[/link]
litmus paper: Filter paper which has been treated with a natural water-soluble dye obtained from lichens. The resulting piece of paper, called 'litmus paper', can be used as a pH indicator. Blue litmus paper turns red under acidic conditions (pH below 4.5) while red litmus paper turns blue under alkaline conditions (pH above 8.3). Neutral litmus paper is purplish in color.
This is litmus powder, which is obtained from oxidation of an extract of lichens in the presence of ammonia
M
macromolecular: Possessing a structure in which all of the atoms within a crystal are linked by chemical bonds.
Examples: Silicon is macromolecular, since all of the atoms of a silicon crystal are chemically bonded into a single unit.
main group: Any of the numbered groups within the Periodic Table.
Example: Group 1, the alkali metals, is a main group.
malleable: capable of being shaped. The term is often used with reference to metals, as in the degree to which they can be shaped by pounding with a hammer.
mass: Mass is the property which reflects the quantity of matter within a sample.
Examples:
mass number: n integer equal to the sum of the number of protons and neutrons of an atomic nucleus.
Examples: 3717Cl has a mass number of 37. Its nucleus contains 17 protons and 20 neutrons.
matter: Matter is the term for any type of material. The word is sometimes used to refer to a pure substance.
Maxwellian distribution: a relation which describes the way molecular energies, as indicated by their speeds, are shared between the molecules of a gas.
Maxwell-Stefan equations: Set of equations that describe the diffusion of solutes and solvent in a concentrated solution. In such a solution, the solutes interact with each other and with the solvent.
mechanism: sequence of steps which occurs during a chemical reaction.
melting: melting is the process by which a substance changes from the solid phase to the liquid phase.
Example: melting of an ice cube into water
melting point: The temperature at which a solid and liquid phase may coexist in equilibrium. The term applies to pure liquids and solutions.
Also Known As: Freezing Point
metal: A substance with high electrical conductivity, luster, and malleability, which readily loses electrons to form positive ions (cations). Metals are otherwise defined according to their position on the Periodic Table, including groupings as alkali metals, alkaline earth metals, transition metals, and rare earth metals.
metalloid: an element with properties intermediate between those of a metal and nonmetal. Metalloids may also be defined according to their location on the Periodic Table.
Also Known As: Semimetal
metallurgy: The science of extracting metals from their ores. Also used to refer to the science of working metals.
miscible: soluble, able to be mixed to form a solution
Common Misspellings: mixable, misible, micible
Examples: Alcohol and water are miscible
mixture: two or more substances which have been combined such that each substance retains its own chemical identity.
Examples: Flour and sugar may be combined to form a mixture.
molality: a unit of concentration, defined to be equal to the number of moles of solute divided by the number of kilograms of solvent.
Examples: The solution made by dissolving 0.10 mol of KNO3 into
molarity: a concentration unit, defined to be the number of moles of solute divided by the number of liters of solution.
Examples: There are 6 moles of HCl in 6 molar HCl or 6M HCl
molar mass: The mass of one mole of a substance, usually expressed in grams or kilograms.
Examples: GMM O2 =
mole: a chemical mass unit, defined to be 6.022 x 1023 molecules, atoms, or some other unit. The mass of a mole is the gram formula mass of a substance.
Examples: 1 mole of NH3 has 6.022 x 1023 molecules and weighs about
mole fraction: a unit of concentration, defined to be equal to the number of moles of a component divided by the total number of moles of a solution.
Examples: In a solution of 1 mol benzene, 2 mol carbon tetrachloride, and 7 mol acetone, the mole fraction of the acetone is 0.7.
molecule: a molecule refers to two or more atoms which have chemically combined to form a single species.
Examples: Examples of molecules include water H2O, oxygen, gas, O2
molecular formula: An expression which states the number and type of atoms present in a molecule of a substance.
Examples: There are
molecular geometry: The molecular geometry describes the shape of a molecule and the relative position of the atomic nuclei of a molecule.
molecular mass: A number equal to the sum of the atomic masses of the atoms in a molecule. The molecular mass gives the mass of a molecule relative to that of the
Examples: The molecular mass of C2H6 is approximately 30 or [(2 x 12) + (6 x 1)]. Therefore the molecule is about 2.5 times as heavy as the
monolithic reactor: Catalytic reactor made of one single piece of solid material. Incorporates a catalytic structure in its often porous structure.
N
Navier-Stokes equations: Equations for the momentum balances coupled to the equation of continuity for a Newtonian incompressible fluid.
Nernst equation: Equation relating the voltage of a chemical cell to its standard voltage and to the concentrations of the reactants and product.
Examples: At
E = E0tot - 0.0591/n x log10{ [ C ]c · [ D ]d / [ A ]a · [ B ]}where E refers to voltage; A, B, C, and D are chemical species; and a, b, c, and d are coefficients in the balanced equation: a A + b B → c C + d D
net ionic equation: Chemical equation for a reaction which lists only those species participating in the reaction.
Examples: The net ionic equation for the reaction that results from mixing
H+(aq) + OH-(aq) → H2O(l)
The Cl- and Na+ ions do not react and are not listed in the net ionic equation
neutral solution: An aqueous solution with a pH of 7.0 ([H+] = 1.0 x 10-
neutralization: Reaction between an acid and a base which produces a neutral solution (pH = 7).
neutron: The particle in the atomic nucleus with a mass = 1 and charge = 0.
Newtonian flow: Flow characterized by a constant viscosity or a viscosity that is independent of the shear rate in the fluid.
noble gas: Any of the elements found in Group 8 at the far right of the Periodic Table.
Examples: Helium, argon, xenon
nonelectrolyte: A substance that does exist in an ionic form in aqueous solution.
Examples: Ethyl alcohol (ethanol) is a nonelectrolyte because it does not ionize when dissolved in water.
nonmetal: One of the elements which do not exhibit metallic properties, generally located in the upper righthand corner of the Periodic Table.
Example: oxygen, nitrogen
nonpolar bond: Type of chemical bond which has no positive or negative 'ends'.
Examples: Found in diatomic and homonuclear molecules, such as O2 and N2.
nonpolar molecule: Molecule which has no separation of charge, so no positive or negative poles are formed.
Examples: O2, CO2, N2
nonspontaneous reaction: A reaction which cannot occur without the input of work from an external source. ΔG > 0 for nonspontaneous reactions at T and P.
nutraceutical: The term nutraceutical was coined in the 1990's by Dr. Stephen DeFelice. He defined nutraceutical as: 'A nutraceutical is any substance that is a food or a part of a food and provides medical or health benefits, including the prevention and treatment of disease. Such products may range from isolated nutrients, dietary supplements and specific diets to genetically engineered designer foods, herbal products, and processed foods such as cereals, soups and beverages. It is important to note that this definition applies to all categories of food and parts of food, ranging from dietary supplements such as folic acid, used for the prevention of spina bifida, to chicken soup, taken to lessen the discomfort of the common cold. This definition also includes a bio-engineered designer vegetable food, rich in antioxidant ingredients, and a stimulant functional food or pharmafood.' Since the term was coined, its meaning has been modified. Health Canada defines nutraceutical as: 'a product isolated or purified from foods, and generally sold in medicinal forms not usually associated with food and demonstrated to have a physiological benefit or provide protection against chronic disease.'
O
octahedral: Possessing the symmetry of a regular octahedron. Having a three-dimensional shape with 6 vertices and 8 faces, where each face forms an equilateral triangle.
octane number: A value used to indicate the resistance of a motor fuel to knock. Octane numbers are based on a scale on which isooctane is 100 (minimal knock) and heptane is 0 (bad knock).
Also Known As: Octane Rating
Examples: A gasoline with an octane number of 92 has the same knock as a mixture of 92% isooctane and 8% heptane.
octet: Group of eight valence electrons surrounding an atom. All noble gases have an octet of valence electrons, with the exception of helium.
octet rule: Refers to the principle that bonded atoms share their eight outer electrons. The octet rule is a 'rule' that is sometimes broken.
olefin: a hydrocarbon containing a carbon-carbon double bond.
Also Known As: Alkene
optical activity: Property in which a substance is able to rotate the plane of a beam of transmitted light; a characteristic of a substance which has a chiral center.
optical density: see absorbance
optical isomerism: Situation in which members of a pair of molecules possessing an identical molecular formula rotate a beam of plane polarized light in opposite directions from each other. Molecules which are capable of optical isomerism have at least one chiral center.
orbital: Electron cloud having an energy state described by given values of the n, l, and ml quantum numbers. An orbital can contain two electrons with paired spins and is often associated with a specific region of an atom.
Examples: The electrons in the 2px orbital of an atom are generally found within a dumbbell-shaped cloud about the x-axis.
organic chemistry: Organic chemistry is the chemistry discipline that is concerned with the study of compounds containing carbon that is chemically bonded to hydrogen. Organic chemistry encompasses the synthesis, identification, modeling, and chemical reactions of such compounds.
osmosis: Process where solvent molecules move through a semipermeable membrane from a dilute solution into a more concentrated solution (which becomes more dilute).
osmotic pressure: name given to the hydrostatic pressure resulting from a concentration gradient across two sides of a surface, such as across a semipermeable membrane.
oxidation number: The oxidation number is the electrical charge that the central atom in a coordination compound would have if all the ligands and electron pairs were removed. Usually the oxidation number has the same value as the oxidation state.
The oxidation number: is represented by a Roman numeral. The plus sign is omitted for positive oxidation numbers. The oxidation number is seen as a superscript to the right of an element symbol (e.g., FeIII) or in parentheses after the element name [e.g., Fe(III)] usually with no space between the element name and the parentheses.
oxidation state: the difference between the number of electrons associated with an atom in a compound as compared with the number of electrons in an atom of the element. In ions, the oxidation state is the ionic charge. In covalent compounds the oxidation state corresponds to the formal charge. Elements are assumed to exist in the zero oxidation state. Examples: in NaCl the oxidation states are Na(+1) and Cl(-1); in CCl4 the oxidation states are C(+4) and each chlorine is Cl(-1)
P
PFR: Plug Flow Reactor. This may be thought of as a long pipe to which the reactants flow in, and the products flow out. In an ideal PFR, the components will be distributed axially, but will have uniform radial distribution.
period: In chemistry, the term period refers to a horizontal row of the periodic table.
periodic table: The periodic table is a tabular arrangement of the chemical elements by increasing atomic number which displays the elements so that one may see trends in their properties. The Russian scientist Dmitri Mendeleev is most often credited with inventing the periodic table (1869) from which the modern table is derived. Although Mendeleev's table ordered the elements according to increasing atomic weight rather than atomic number, his table illustrated recurring trends or periodicity in the element properties.
Also Known As: Periodic Chart, Periodic Table of the Elements, Periodic Table of the Chemical Elements
The periodic table is a way of organizing the chemical elements.
periodicity: In the context of chemistry and the periodic table, periodicity refers to trends or recurring variations in element properties with increasing atomic number. Periodicity is caused by regular and predictable variations in element atomic structure.
petrochemistry: Petrochemistry is the scientific study of the chemical reaction involved in converting petroleum and natural gas into other materials and products.
pH: pH is a measure of hydrogen ion concentration; a measure of the acidity or alkalinity of a solution. Aqueous solutions at
phase: a physically distinctive form of matter, such as a solid, liquid, gas or plasma. A phase of matter is characterized by having relatively uniform chemical and physical properties. Phases are different from states of matter. The states of matter (e.g., liquid, solid, gas) are phases, but matter can exist in different phases yet the same state of matter. For example, mixtures can exist in multiple phases, such as an oil phase and an aqueous phase.
phase transition: The transformation of a system from one phase to another. A phase transition is characterized by a significant change in one or more physical property. Examples: freezing of a liquid into a solid, vaporization of a liquid into a gas.
Also Known As: Phase Change
This diagram illustrates the different phase transitions or phase changes between different states of matter.
pheromone: A chemical secreted externally by an organism to send information to members of the same species.
Examples: musk from deer
physical chemistry: Physical chemistry is the branch of chemistry that is concerned with the application of physics to chemical systems. This may involve the application of the principles of thermodynamics, quantum mechanics, quantum chemistry, statistical mechanics and kinetics to the study of chemistry.
Also Known As: Chemical Physics
physics: Physical chemistry is the branch of chemistry that is concerned with the application of physics to chemical systems. This may involve the application of the principles of thermodynamics, quantum mechanics, quantum chemistry, statistical mechanics and kinetics to the study of chemistry.
Also Known As: Chemical Physics.
physisorption: See adsorption.
phytochemical: Substance derived from a plant. The term is generally reserved for molecules with biological activity.
piezoelectric: A material that generates an electric charge when mechanically deformed. Conversely, when an external electric field is applied to piezoelectric materials they mechanically deform.
Examples: quartz, living bone, ultra-sonic transducers to create underwater SONAR
pnictogen: a member of the nitrogen group of elements, Group 15 of the periodic table (formerly numbered as Group V or Group VA). This group consists of nitrogen, phosphorus, arsenic, antimony, bismuth, and ununpentium. Binary compound from this group are termed pnictides. The pnictogens are noted for their ability to form stable compound, thanks to their tendency to form double and triple covalent bonds.
Pnictogens are members of the nitrogen group of elements.
Poiseuille’s law: Equation that relates the mass rate of flow in a tube as proportional to the pressure difference per unit length and to the fourth power of the tube radius. The law is valid for fully developed laminar flow.
polymer: A large molecule made up of chains or rings of linked monomer units. Polymers usually have high melting and boiling points.
Examples: PVC (poly vinyl chloride), polystyrene, cellulose
potential energy: Potential energy is that energy which an object has because of its position. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy.
Example: If you lift a mass m by h meters, its potential energy will be mgh, where g is the acceleration due to gravity.
precipitate: to form an insoluble compound either by reacting two salts or by changing the temperature to affect the solubility of the compound. Also the name given to the solid that is formed as a result of a precipitation reaction.
Example: Mixing silver nitrate and sodium chloride in water will cause silver chloride to precipitate out of solution as a solid.
This diagram illustrates the process of chemical precipitation.
pressure: Pressure is a measure of the force applied over a unit area. Pressure often is expressed in units of pascals or pounds per square inch. In equations, pressure is denoted by the symbol 'P'.
principal energy level: The energy level denoted by the principal quantum number n. The first element in a period of the Periodic Table introduces a new principal energy level.
principal quantum number: The quantum number denoted by n. The principal quantum number is cited first in the set of four quantum numbers associated with an electron. The principal quantum number has the greatest effect on the energy of the electron.
principal species: The major species in which a cation is present, under a specified set of conditions. Although usually applied to cations, the term 'principal species' may also be applied to anions.
Examples: Zinc (II) may be present as Zn2+, Zn(NH3)2+, Zn(OH)2, etc. Equilibrium considerations may be used to determine which cation species is the principal species. For anions, at pH 8, the HCO3- ion is the principal species in the H2CO3—HCO3-—CO32- system.
prion: A protein particle that is capable of causing an infection or disease. Like viruses, prions are not capable of reproduction by themselves. Unlike viruses, prions do not contain genetic material (DNA or RNA).
product: A substance that is formed as the result of a chemical reaction.
Examples: AgCl (s) is the product of the reaction Ag+ (aq) + Cl- (aq) → AgCl (s).
proof: Twice the volume percentage of ethyl alcohol (ethanol) in an alcoholic beverage.
Example: An alcoholic beverage that is 40% ethyl alcohol by volume is referred to as being '80 proof'.
property: A characteristic of a sample of matter that is fixed by its state.
Examples: Properties of a sample of hydrogen gas include the density and energy of a mole of H2 at 1 atm and
protein: A polypeptide or molecule made up of polypeptides.
Examples: Albumin, hemoglobin, keratin.
proton: A component of an atomic nucleus with a mass defined as 1 and a charge of +1. The nucleus of a hydrogen atom. The H+ ion.
protonation: the addition of a proton to an atom, molecule, or ion. Protonation is different from hydrogenation in that during protonation a change in charge of the protonated species occurs, while the charge is unaffected during hydrogenation. Example: formation of the ammonium group where NH4+ is formed by protonation of ammonia NH3.
psi (Ψ): The amplitude or height of an electron wave at various points in space and denoted by the Greek letter Ψ.
p-type semiconductor: Type of semiconductor in which current passes through a solid via electron flow into positive 'holes' in a crystal. The holes are introduced using electron-deficient impurity atoms (doped crystal).
pyramidal: Adjective used to describe the geometry of a molecule in which one atom is positioned directly above the center of an equilateral triangle formed by the other three atoms.
Example: NH3 (ammonia) exhibits pryamidal geometry.
Q
qualitative analysis: The determination of the nature of the chemical species in a sample.
Examples: She used qualitative analysis to find that the solution contained Cu2+ and Cl- ions.
quantitative analysis: Quantitative analysis refers to the determination of how much of a given component is present in a sample.
Examples: She used quantitative analysis to find that the ore contained 42.88% silver by mass. Qualitative analysis tells 'what' is in a sample, while quantitative analysis is used to tell 'how much' is in a sample.
quantum mechanics: The physical science used to calculate and analyze the energies and spatial distributions of small particles confined to very small regions of space.
quantum number: A number used when describing the energy levels available to atoms and molecules. An electron in an atom or ion has four quantum numbers to describe its state.
quantum theory: The general theory which describes the allowed energies of atoms and molecules.
R
RANS: Reynolds-averaged Navier-Stokes, which implies time averaging of the velocity fluctuations in turbulent flow. The Reynolds’ stresses obtained by this averaging have to be expressed with an additional set of equations. Turbulence models like the k-ε and k-ω models belong to this class.
reactant: Starting material in a chemical reaction.
Examples: H2 and O2 are reactants in the reaction H2(g) + 1/2 O2(g) --> H2O(l).
reaction: A chemical change which forms new substances.
Examples: The chemical reaction H2(g) + ½ O2(g) → H2O(l) describes the formation of water from its elements.
relative density: Dimensionless ratio of the densities of two materials. It is similar to specific gravity, in which the reference material is water.
reciprocal rule: The relationship between equilibrium constants for forward (Kf) and reverse (Kr) reactions such that Kr = 1/Kf.
redox reaction: Any chemical reaction which involves oxidation and reduction.
redox titration: Titration of a reducing agent by an oxidizing agent or titration of an oxidizing agent by a reducing agent.
reducing agent: A chemical species which provides electrons for another chemical species.
Examples: Metallic zinc, Zn(s), is the reducing agent in the reaction:
Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g).
reduction: A half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons.
Examples: The H+ ions, with an oxidation number of +1, are reduced to H2, with an oxidation number of
relative humidity: A measure of the amount of water in air divided by the amount of water that the air could hold, expressed as 100 x P/P0, where P is the pressure of the water vapor in the air and P0 is the equilibrium vapor pressure of water at the same temperature.
Example: A relative humidity of 95% indicates that there is 95/100ths as much water in the air as that air is capable of holding at that temperature.
rem: A unit of absorbed radiation. One rem is equal to n times the number of rads, where the factor n is dependent on the type of radiation which is being absorbed.
resonance: Term in chemistry used to explain properties of the octet rule when a single Lewis structure is inadequate. Resonance structure is an average of two of more Lewis structures which differ only in the position of their electrons. These species are said to exhibit resonance.
Two Lewis structures or electron dot diagrams for the nitrite ion in resonance
reverse osmosis Process: in which purified water is obtained from a salt solution. Water passes through a semipermeable membrane under pressure.
Reynold's Number: This is a number which characterises flow. If the Reynold's number is low (under approximately 1800) then the flow is said to be laminar. This may be thought of as the fluid flowing in layers. If the Reynold's number is high (over approximately 2300) then the flow is said to be turbulent. Turbulent flow is considered to be well mixed.
RNA: The acronym for ribonucleic acid. Forms of RNA include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). RNA codes for amino acid sequences, which may be combined to form proteins. Where DNA is used, RNA acts as an intermediary, transcribing the DNA code so that it can be translated into proteins.
roasting: A process in metallurgy in which a sulfide ore is heated in air. The process may convert a metal sulfide to a metal oxide or to a free metal.
Example: Roasting ZnS may yield ZnO; roasting HgS may yield free Hg metal.
S
salt: sometimes 'salt' simply refers to table salt, which is sodium chloride. Usually the term is applied to an ionic compound produced by reacting an acid with a base.
Examples:
Table salt is sodium chloride, shown here
NaCl, KCl, CuSO4
saponification: Usually, a process by which triglycerides are reacted with sodium or potassium hydroxide to produce glycerol and a fatty acid salt, called 'soap'.
Lipids that contain fatty acid ester linkages can undergo hydrolysis. This reaction is catalyzed by a strong acid or base. Saponification is the alkaline hydrolysis of the fatty acid esters.
Example: An example of the reaction is:
saturated: as in a saturated compound: A substance in which the atoms are linked by single bonds. A fully saturated compound contains no double or triple bonds.
Example: ethane (C2H6)
Definition #2: as in a saturated solution. In this context, saturated refers to a point of maximum concentration, in which no more solute may be dissolved in a solvent.
science: Science is the systematic study of the natural world using the scientific method. The word for science is derived from the Latin word scientia for knowledge.
scientific method: The scientific method is a system of acquiring knowledge through observation and the experimental testing of hypotheses. The scientific method is based on obtaining and analyzing empirical evidence to support the reasoning process.
solid: state of matter characterized by particles arranged such that their shape and volume are relatively stable. The constituents of a solid tend to be packed together much closer than the particles in a gas or liquid.
Examples: a brick, a penny, a piece of wood, a chunk of aluminum metal
Most metals, like this aluminum, are solids at room temperature.
solubility: the maximum quantity of a substance that may be dissolved in another. The maximum amount of solute that may be dissolved in a solvent.
solute: The substance that is dissolved in a solution. For solutions of fluids, the solvent is present in greater amount than the solute.
Examples: salt in water
solution: A solution is a homogeneous mixture of two or more substances. A solution may exist in any phase.
Solution Examples: An example of a solid solution is brass. An example of a liquid solution is aqueous hydrochloric acid (HCl in water). An example of a gaseous solution is air.
These are colored transition metal solutions.
solvent: The component of a solution that is present in the greatest amount. It is the substance in which the solute is dissolved.
Examples: The solvent for seawater is water. The solvent for air is nitrogen
specific gravity: This is the ratio of the density of a substance to the density of water.
Example: The specific gravity of pure water is 1. Specific gravity is a unitless value.
specific heat: Specific heat is the amount of heat needed to raise the temperature of one gram of a substance by
specific surface area: Internal surface area of a porous structure given in area per unit volume, which yields the unit one over unit length. Often used to characterize the structure of porous catalysts.
specific weight: Weight per unit volume of a material.
spectrum: The characteristic wavelengths of electromagnetic radiation (or a portion thereof) that is emitted or absorbed by an object or substance, atom, or molecule.
spin: in physics and chemistry (quantum mechanics), spin represents an intrinsic property of a particle relating to its angular momentum.
spin quantum number (Ms): The fourth quantum number denoted by ms. The spin quantum number indicates the orientation of the intrinsic angular momentum of an electron in an atom. The only possible values of a spin quantum number are +½ or -½ (sometimes referred to as 'spin up' and 'spin down').
spontaneous process: A process that will occur without any energy input from the surroundings. A process that will occur on its own.
standard solution: Any solution which has a precisely known concentration. Similarly, a solution of known concentration has been standardized.
standard temperature and pressure: STP corresponds to 273 K (0° Celsius) and 1 atm pressure. STP is often used for measuring gas density and volume.
state of matter: one of the ways in which matter can interact with itself to form a homogeneous phase.
Examples: solid, liquids, gases, plasma
sterling silver: A silver alloy containing 92.5% pure silver and 7.5% other metal, usually copper.
steroid: A steroid is a terpenoid lipid that is characterized by having a carbon skeleton formed from four fused rings. The rings typically are arranged in a 6-6-6-5 manner. Steroids are distinguished from each other based on the functional groups that are attached to the rings.
Examples: estrogen, progesterone, testosterone, cholesterol
stock solution: A Stock Solution is a concentrated solution that will be diluted to some lower concentrated for actual use. Stock solutions are used to save preparation time, conserve materials, reduce storage space, and improve the accuracy with which working solutions are prepared.
stoichiometry: Stoichiometry is the study of the relationships or ratios between two or more substances undergoing a physical or chemical change (chemical reaction).
streamline-diffusion stabilization: A numerical technique for stabilization of the numeric solution to a convection-dominated PDE by artificially adding diffusion in the direction of the streamlines.
strong acid: A strong acid is an acid that is completely dissociated in an aqueous solution.
Examples: HCl
strong base: A strong base is a base that is completely dissociated in an aqueous solution.
Examples: KOH, NaOH
sublimation: Sublimation is the transition from the solid phase to the gas phase without passing through an intermediate liquid phase. This endothermic phase transition occurs at temperatures and pressures below the triple point.
Example: Dry ice is solid carbon dioxide. At room temperature and pressure, it sublimates into carbon dioxide vapor.
These pellets of dry ice are sublimating in air.
supercooling: Supersaturated or Supercooling is the condition in which a liquid has been cooled to a temperature below that at which crystallization normally would occur, without the solid resulting.
Also Known As: Supercooling
Example: Water may be supercooled or supersaturated several degrees past its freezing point without ice forming, as long as no dust or other crystallization points are available.
supernate: Supernate is the liquid which remains above the solid produced by a precipitation reaction.
surfactant: Surfactant is the word that combines the terms "surface active agent". Chemical species that acts as wetting agents to lower the surface tension of a liquid and allow for increased spreadability. This can be at a liquid-liquid interface or a liquid-gas interface.
Also Known As: tenside
switch function: Conditional function that gives a smooth onset of a variable, for example from 0 to 1 or from 1 to 0. Often used for phase changes or saturation.
T
tautomer: Tautomers are organic compounds that are interconvertible by a chemical reaction called tautomerization. Usually, the reaction involves the migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond.
temperature: Temperature is the property of matter which reflects the quantity of energy of motion of the component particles. There are several scales used to measure this value (e.g., Kelvin, Celsius, Fahrenheit).
Examples: The temperature of the solution was
terpene: C10 and C15 are volatile organic compounds derived from plants. Terpenes are generally associated with characteristic fragrances. Some terpenes are alcohols (e.g., menthol from peppermint oil) and some terpenes are aldehydes (e.g., citronellal). Terpenes are made up of isoprene (C5) units.
Examples: nepetalactone from catnip, limonene from lemon oil, zingiberene from ginger
tetrahedral: Tetrahedral is a descriptor of the geometry of a molecule in which a central atom forms four bonds which are directed toward the corners of a regular tetrahedron. Tetrahedral geometry forms a solid with four vertices and four sides, all of which are equilateral triangles.
theoretical yield: Theoretical Yield is the quantity of a product obtained from the complete conversion of the limiting reactant in a chemical reaction. Theoretical yield is commonly expressed in terms of grams or moles.
thermal: Thermal is an adjective pertaining to or relating to heat.
Examples: The thermal properties of a material refer to characteristics relating to heat, such as the ability to absorb or radiate heat.
thermochemistry: Thermochemistry is the scientific study of heat that is released or absorbed during chemical changes.
thermodynamics: Thermodynamics is the scientific study of work, heat, and the related properties of chemical and mechanical systems.
titrant: Titrant is a solution of known concentration which is added (titrated) to another solution to determine the concentration of a second chemical species.
titration: Titration is the process in which one solution is added to another solution such that it reacts under conditions in which the added volume may be accurately measured. Titrations are most commonly associated with acid-base reaction, but they may involve other types of reactions as well.
transition metal: A Transition Metal is an element from the B group of the periodic table. Transition metals have partially filled d sublevel orbitals.
Example: scandium, zirconium, tantalum, molydenum, manganese, copper, zinc
translational energy: Translational Energy is the energy of motion through space.
Examples: Falling objects have translational energy; sliding objects have translational energy.
transmute: To transmute is to change from one form or substance into another; to transform or convert.
Examples: Turning lead into gold
triangular bipyramid: A triangular bipyramid is a solid which has five vertices and six sides. The solid may be thought of as consisting of two pyramids which are fused through a base that is an equilateral triangle.
triboluminescence: Triboluminescence is luminescence (light) triggered by mechanical energy or electrical energy from a mechanical action such as friction.
Examples: many minerals, such as quartz, will glow when scratched; sucrose emits a blue light when crushed.
triple bond: A triple bond is three electron pairs which are shared between two bonded atom.
Examples: A triple bond exists between the atoms of divalent nitrogen, N2.
triple point: Triple Point is the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium. A specific case of phase equilibrium.
Examples: The triple point for water is at 0.01° Celsius at
ultraviolet radiation: Ultraviolet radiation is light having a wavelength greater than 10 nm but less than 400 nm.
Also Known As: UV radiation
unit cell: A unit cell is the smallest unit of a crystal, which, if repeated, could generate the whole crystal.
unpaired electon: An unpaired electron is a single electron occupying an orbital by itself.
unsaturated: When referring to solutions, being able to dissolve more solute. When referring to organic compounds, containing double or triple carbon-carbon bonds.
Examples: Examples of saturated organic molecules include HC=CH and H2C=O
useful work: In the reaction H2O (l) → H2O (g), since the volume of the gas is larger than the volume of the liquid, work of expansion will be required to push back the air in order to make room for the water vapor. In this case, the useful work is the work done during the change which is in excess of the work of expansion.
V
valence: Valence is typically, the number of electrons needed to fill the outermost shell of an atom. Because exceptions exist, the more general definition of valence is the number of electrons with which a given atom generally bonds or number of bonds an atom forms. (Think iron, which may have a valence of 2 or a valence of 3.)
Examples: A neutral carbon atom has 6 electrons, with an electron shell configuration of 1s22s22p2. Carbon has a valence of 4, since 4 electrons can be accepted to fill the 2p orbital.
Van der Waals forces: Van der Waals Forces are the weak forces which contribute to intermolecular bonding.
Examples: hydrogen bonding, dispersion forces, dipole-dipole interactions.
van't Hoff rule: Van't Hoff Rule is a method of predicting the maximum number of enantiomers of an optically active molecule: 2n, where 'n' is the number of stereogenic centers.
vapor: Vapor is a condensable gas.
Examples: Examples include air, steam, oxygen and any other gases which may be condensed into liquid form.
vapor pressure: The pressure exerted by a vapor in equilibrium with the solid or liquid phase of the same substance. Also, the partial pressure of the substance in the atmosphere above the solid or the liquid.
vaporization: the phase transition of a substance from the liquid phase to the gas phase.
Examples: evaporation, boiling
Boiling is a type of vaporization.
vicinal: Vicinal is a term used to describe the location of two identical chemical groups or atoms which are bonded to adjacent carbon atoms.
Examples: a vicinal dihalide
vinyl alcohol: Vinyl Alcohol is an alcohol with structure: CH2=CH-OH
vinyl group: Vinyl Group is the CH2=CH- group.
vitrification: Vitrification is the process of converting a material into a glassy amorphous solid that is free from crystalline structure. This can be achieved through the addition of heat or introduction of an additive. Vitrification occurs at the glass transition temperature which is lower than the melting point.
volatile: "Volatile" refers to a substance that vaporizes readily. Volatility is a measure of how readily a substance vaporizes.
volume: Volume is the quantity of three-dimensional space occupied by a liquid, solid, or gas. Common units used to express volume include liters, cubic meters, gallons, milliliters, teaspoons and ounces. Many other units exist.
W
wall function: Semi-empirical expression for the anisotropic flow close to a solid surface used in turbulence models. Often based on negligible variations in pressure gradient in the direction tangential to the surface.
weak acid: A weak acid is an acid that is partially dissociated in an aqueous solution.
Examples: CH3COOH
weak base: A weak base is a base that is partially dissociated in an aqueous solution.
Examples: NH4OH
wedge-and-dash projection: Wedge and Dash Projection is a means of representing a molecule (drawing) in which three types of lines are used in order to represent the three-dimensional structure: (1) solid lines to represent bonds which are in the plane of the paper, (2) dashed lines to represent bonds that extend away from the viewer, and (3) wedge-shaped lines to represent bonds oriented facing the viewer.
working solution: Working Solution is a name given to a chemical solution made for actual use in the lab, usually made from diluting or combining stock or standard solutions.
Wurtz reaction: Wurtz Reaction is the coupling of two alkyl halide molecules to form an alkane.
X
xenobiotic: Xenobiotic is any chemical that would not normally be found in a living organism or be expected to be produced by it. Examples: organs that are transplanted across species, genes from different organisms, dioxin in humans, antibiotics in humans since we do not produce them ourselves.
xenon: xenon is an element with an atomic number of 54 and atomic weight of 131.29. It is an odorless inert gas that is used to fill cathode ray tubes.
Xenon normally is a colorless gas, but it emits a blue glow when excited by an electrical discharge, as seen here.
X group: 'X' is used to denote a halogen in the structural formula of a molecule (usually organic).
x-rays: X-rays are light rays with a wavelength from 0.01 to 1.0 nanometers.
Also Known As: X radiation.
x-ray crystallography: X-Ray Crystallography is an analytical method in which x-ray diffraction patterns are used to determine the three-dimensional arrangement of atoms in a crystal. Many crystal used for x-ray crystallography are less than
X-ray diffraction pattern of a crystallized protein.
x-ray diffraction pattern: X-Ray Diffraction Pattern is an interference pattern created by x-rays as they pass through a material, such as a crystal.
x-ray tube: An X-Ray tube is a type of cathode ray tube that focuses electrons onto a metal target, thus causing the metal to emit x-rays.
Y
yield: Yield is the quantity of product obtained from a reaction.
ytterbium ytterbium: is the rare earth element with an atomic number of 70 and atomic weight of 173.04. The malleable metal is a component of x-ray sources.
Ytterbium is a lustrous bright silvery metal.
yttrium yttrium: is an element element with an atomic number of 39 and atomic weight of 88.90585. It is a dark gray metal that is used to make alloys for nuclear technology because the element has a high neutron transparency.
Yttrium is a lustrous silver metal. Shavings of the metal can ignite spontaneously in air.
Z
Z (zusammen): Z or Zusammen is notation for a stereochemical arrangement where all of the higher-ranking substituent groups are located on the same side of the double bond.
Zaitsev rule: Zaitsev Rule is an organic chemistry rule which states that the major product in the formation of alkenes from elimination reactions will be a more highly substituted alkene or the alkene with more substituents of the carbon atoms of the double bond.
zeolite: Zeolites are a type of silicate mineral. Zeolites are often used to soften water by cation exchange.
zero order reaction: A Zero Order reaction is a reaction whose rate is independent of the concentration of reactants.
zwitterion: Zwitterion is the dipolar form of an amino acid which occurs when H+ ion is transferred from an acid group to an amine group.
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