Chemistry Definitions
Calorie Unit of thermal
energy; the amount of energy required to raise the temperature of 1 gram of
water 1 degree °C or K at standard pressure.
Cannizzaro reaction The reaction in
which aldehydes that do not have a hydrogen attached to the carbon adjacent to
the carbonyl group, upon encountering strong alkali, readily form an alcohol
and an acid salt.
Canonical form 1. A
resonance structure for a cyclic compound in which the bonds do not intersect. 2.
See contributing structure.
Capacity In chromatography, a measurement
used in ion-exchange systems to express the adsorption ability of the
ion-exchange materials.
Capillary action The spontaneous floe of
liquid into a narrow tube or porous material.
Carbon nanotubes Cylindrical
molecules (sealed at both ends with a convex arrangement of atoms) composed of
carbon with a diameter of around 1 nanometer and lengths up to a few
micrometers. Single-walled nanotubes may be conducting or semiconducting,
depending on the diameter and chirality of the tube. Multiwall nanotubes
containing coaxial shells of the elemental single-wall nanotubes are also possible.
Carrier A substance that, when associated
with a trace of another substance, will carry the trace with it through a
chemical or physical process.
Carrier gas In gas chromatography, a gas used as
an eluant for extracting the sample from the column as the gas passes through.
Also known as eluant gas.
Catalysis A phenomenon in which a relatively
small amount of substance augments the rate of a chemical reaction without
itself being consumed.
Catalyst Substance that
alters the velocity of a chemical reaction and may be recovered essentially
unaltered in form and amount at the end of the reaction.
Catalyst carrier A neutral
material used to support a catalyst, such as activated carbon, diatomaceous
earth, or activated alumina.
Catalyst selectivity 1. The
relative activity of a catalyst in reference to a particular compound in a
mixture. 2. The relative rate of a single reactant in competing reactions.
Cathode The electrode at which reduction
takes place in an electrochemical cell, that is, a cell through which electrons
are being forced.
Cathodic polarization Portion of
electric cell polarization occurring at the cathode.
Catholyte Electrolyte
adjacent to the cathode in an electrolytic cell.
Cation A positively
charged atom or group of atoms, or a radical which moves to the negative pole
(cathode) during electrolysis.
Cation analysis Qualitative
analysis for cations in aqueous solution.
Cation exchange A chemical
reaction in which hydrated cations of a solid are exchanged, equivalent for
equivalent, for cations of like charge in solution.
Cation exchange resin A highly
polymerized synthetic organic compound consisting of a large, nondiffusible
anion and a simple, diffusible cation, which later can be exchanged for a
cation in the medium in which the resin is placed.
Cationic detergent A member of a
group of detergents that have molecules containing a quaternary ammonium salt
cation with a group of 12 to 24 carbon atoms attached to the nitrogen atom in
the cation; an example is alkyltrimethyl ammonium bromide.
Cationic hetero atom A positively
charged atom, other than carbon, in an otherwise carbon atomic chain or ring.
Cationic polymerization A type of
polymerization in which Lewis acids act as catalysts.
Cationic reagent A
surface-active agent with active positive ions used for ore beneficiation
(flotation via flocculation); an example of a cationic reagent is cetyl trimethyl
ammonium bromide.
Chain isomerism A type of
molecular isomerism seen in carbon compounds; as the number of carbon atoms in
the molecule increases, the linkage between the atoms may be a straight chain
or branched chains producing isomers that differ from each other by possessing
different carbon skeletons.
Chain reaction A chemical
reaction in which many molecules undergo chemical reaction after one molecule
becomes activated.
Chelate A molecular
structure in which a heterocyclic ring can be formed by the unshared electrons
of neighboring atoms.
Chelating agent An organic
compound in which atoms form more than one coordinate bond with metals in
solution.
Chelating resin Any of the
ion-exchange resins with unusually high selectivity for specific cations; for
example, phenol-formaldehyde resin with 8-quinolinol replacing part of the
phenol, particularly selective for copper, nickel, cobalt, and iron(III).
Chelation A chemical process involving
formation of a heterocyclic ring compound which contains at least one metal
cation or hydrogen ion in the ring.
Chemical energy Energy of a
chemical compound which, by the law of
conservation
of energy, must undergo a change equal and opposite to the change of heat
energy in a reaction; the rearrangement of the atoms in reacting compounds to
produce new compounds causes a change in chemical energy.
Chemical equilibrium A condition in
which a chemical reaction is occurring at equal rates in its forward and
reverse directions, so that the concentrations of the reacting substances do
not change with time. Also known as equilibrium.
Chemical indicator 1. A
substance whose physical appearance is altered at or near the end point of a
chemical titration. 2. A substance whose color varies as the
concentration of hydrogen ions in the solution to which it is added varies. Also
known as indicator.
Chemical inhibitor A substance
capable of stopping or retarding a chemical reaction.
Chemical kinetics That branch of
physical chemistry concerned with the mechanisms and rates of chemical reactions.
Also known as reaction kinetics.
Chemical microscopy Application of
the microscope to the solution of chemical problems.
Chemical polarity Tendency of a
molecule, or compound, to be attracted or repelled by electrical charges
because of an asymmetrical arrangement of atoms around the nucleus.
Chemical potential In a
thermodynamic system of several constituents, the rate of change of the Gibbs
function of the system with respect to the change in the number of moles of a
particular constituent.
Chemical reactivity The tendency of
two or more chemicals to react to form one or more products differing from the
reactants.
Chemical relaxation The
readjustment of a chemical system to a new equilibrium after the equilibrium of
a chemical reaction is disturbed by a sudden change, particularly in an
external parameter such as pressure or temperature.
Chemical shift Shift in a
nuclear magnetic-resonance spectrum resulting from diamagnetic shielding of the
nuclei by the surrounding electrons.
Chiral center An atom in a
molecule that is attached to four different groups.
Chirality The handedness
of an asymmetric molecule.
Chiral molecules Molecules which
are not superposable with their mirror images.
Chiral nanotube A carbon
nanotube formed from a graphite sheet that is rolled up so that the succession
of hexagons of carbon atoms on a particular cylinder makes an angle with the
axis of the nanotube
Column chromatography Chromatographic
technique of two general types: packed columns usually contain either a
granular adsorbent or a granular support material coated with a thin layer of
high-boiling solvent (partitioning liquid); open-tubular columns contain a thin
film of partitioning liquid on the column walls and have an opening so that gas
can pass through the center of the column.
Combination reaction A chemical
reaction in which two reactions combine to form a single product.
Combination vibration A vibration of
a polyatomic molecule involving the simultaneous excitation of two or more
normal vibrations
Combustion 1. The burning of gas, liquid, or
solid, in which the fuel is oxidized, evolving heat and often light. 2. This
is the combining of a substance with oxygen.
Combustion efficiency The ratio of
heat actually developed in a combustion process to the heat that would be
released if the combustion were perfect.
Complexation reaction A chemical
reaction that takes place between a metal ion and a molecular or ionic entity
known as a ligand that contains at least one atom with an unshared pair of
electrons.
Complex chemical reaction A chemical
system in which a number of chemical reactions take place simultaneously,
including reversible reactions, consecutive reactions, and concurrent or side
reactions.
Complex compound Any of a group
of chemical compounds in which a part of the molecular bonding is of the
coordinate type. Also known as coordination complex.
Complexing agent A substance
capable of forming a complex compound with another material in solution.
Complexometric titration A technique of
volumetric analysis in which the formation of a colored complex is used to
indicate the end point of a titration. Also known as chelatometry. Also spelled
compleximetric titration.
Composition The elements or compounds making up a material
or produced from it by analysis.
Compound 1. A
substance whose molecules consist of unlike atoms and whose constituents cannot
be separated by physical means. Also known as chemical compound. 2. A
substance made up of two or more elements chemically combined
Concentration In solutions,
the mass, volume, or number of moles of solute present in proportion to the
amount of solvent or total solution.
Concentration cell 1. Electrochemical
cell for potentiometric measurement of ionic concentrations where the electrode
potential electromotive force produced is determined as the difference in emf
between a known cell (concentration) and the unknown cell. 2. An
electrolytic cell in which the electromotive force is due to a difference in
electrolyte concentrations at the anode and the cathode.
Concentration gradient The graded
difference in the concentration of a solute throughout the solvent phase.
Concentration polarization That part of
the polarization of an electrolytic cell resulting from changes in the electrolyte
concentration due to the passage of current through the solution.
Concentration potential Tendency for a
univalent electrolyte to concentrate in a specific region of a solution.
Condensation Transformation
from a gas to a liquid.
Condensation polymer A
high-molecular-weight compound formed by
condensation
polymerization.
Condensation polymerization The stepwise
reaction between functional groups of reactants in which a
high-molecular-weight polymer is formed only after a large number of steps, for
example, the reaction of dicarboxylic acids with diamines to form a polyamide.
Condensation reaction One of a class
of chemical reactions involving a combination between molecules or between
parts of the same molecule.
Condensation resin A resin formed
by polycondensation.
Condensation temperature In
boiling-point determination, the temperature established on the bulb of a
thermometer on which a thin moving film of liquid coexists with vapor from
which the liquid has condensed, the vapor phase being replenished at the moment
of measurement from a boiling-liquid phase.
Condensed phase Either the
solid or liquid phase of a material.
Condensed system A chemical
system in which the vapor pressure is negligible or in which the pressure
maintained on the system is greater than the vapor pressure of any portion.
Conductance coefficient The ratio of
the equivalent conductance of an
electrolyte,
at a given concentration of solute, to the limiting equivalent conductance of
the electrolyte as the concentration of the electrolyte approaches 0.
Conductimetry The
scientific study of conductance measurements of solutions; to avoid
electrolytic complications, conductance measurements are usually taken with
alternating current.
Conductometric titration A titration in which electrical conductance of
a solution is measured during the course of the titration.
Conjugate acid-base pair An acid and a
base related by the ability of the acid to generate the base by loss of a
proton.
Conjugated diene An acyclic
hydrocarbon with a molecular structure containing two carbon-carbon double
bonds separated by a single bond.
Conjugated polyene An acyclic
hydrocarbon with a molecular structure containing alternating carbon-carbon
double and single bonds.
Coordinate bond See coordinate
valence.
Coordinated complex See coordination
compound.
Coordinate valence A chemical bond
between two atoms in which a shared pair of electrons forms the bond and the
pair has been supplied by one of the two atoms. Also known as coordinate bond;
dative bond.
Coordination chemistry The chemistry
of metal ions in their interactions with other molecules or ions.
Coordination complex See complex
compound.
Coordination compound A compound with a central atom or ion and a
group of ions or molecules surrounding it. Also known as coordinated complex;
Werner complex.
Copolymer A mixed polymer, the product of polymerization
of two or more substances at the same time.
Copolymerization A polymerization reaction that forms a
copolymer.
Corrosion Corrosion
is an undesired process where a metal is converted to one of its compounds,
e.g. rusting.
Corrosion inhibitor A compound or
material deposited as a film on a metal surface that either provides physical
protection against corrosive attack or reduces the open-circuit potential
difference between local anodes and cathodes and increases the polarization of
the former.
