GLOSSARY 457rate of reaction The speed of a reaction at an instant;
usual units are mol dm^3 s^1.reaction intermediate A species that is produced and
consumed during an overall reaction.reaction mechanism The collection of elementary
reactions making up an overall reaction.
redox couple The oxidized and reduced species in a half-
reaction.reducing agent A substance which causes another sub-
stance to be reduced in a chemical reaction and it itself is
oxidized.resonance Mixing Lewis structures to obtain the actual
structure of a species.room temperature and pressure (RTP) In this book,
taken as 20 °C and 1 atm pressure.salt A substance made by the neutralisation of an acid with
a base.saturated hydrocarbon A hydrocarbon that contains no
carbon–carbon multiple bonds and cannot react with
hydrogen, e.g. an alkane.semiconductor A substance that is not a good conductor
of electricity at room temperature, but becomes con-
ducting if certain other elements are added to it in small
amounts.specific heat capacity A quantity, symbolized C, which
is equal to the amount of heat energy required to raise the
temperature of 1 g of material by 1 °C; units are
Jg^1 °C^1 or J g^1 K^1. See the website.spectrometer An instrument which measures the fre-
quencies and intensities of emitted or absorbed light. (A
simpler hand-held instrument is called a spectro-
scope.)
spectrum The pattern of frequencies (and the intensities)
of light that is emitted (emission spectrum) or absorbed
(absorption spectrum) by a species.standard ambient temperature and pressure (SATP)
25 °C (298 K) and 100 kPa.
standard deviation A calculated quantity which measures
the precision of a set of repeat results. See the website.standard enthalpy of formation (H^ —f) The standard
enthalpy change that accompanies the formation of
1 mol of a substance from its constituent elements in
their standard states.
standard state A pure form of a substance at 1 atm pressure.standard temperature and pressure (STP) 0 °C and
1 atm pressure.stoichiometric point Another name for equivalence point.
strong acid An acid that is completely ionized in solution.strong base A base that is completely ionized in solution.strongly acidic solution A solution with a pH below 3.strongly basic solution A solution with a pH above 12.sublimation Changing directly from a solid to a vapour.substitution reaction A reaction in which an atom or
group of atoms replaces another atom or group of atoms
in a molecule.systematic errors Errors which cause measurements
either to be higher or lower than the true value, and
which cannot be averaged out.titration A technique in which a solution of known concen-
tration (a standard solution) is reacted with a solution of
unknown concentration, until equivalent quantities have
reacted.transition metal A group of elements found between
groups 2 and 13 of the Periodic Table.
uncertainty(in a measurement) A quantity which indi-
cates the degree of doubt in a measurement. It is the part
of a measurement given after the sign. For example, if
a temperature is recorded as 25.5 0.4 °C, the uncer-
tainty is 0.4 °C.unsaturated hydrocarbon A hydrocarbon that contains
carbon–carbon multiple bonds and can react with
hydrogen, e.g. an alkene or alkyne.Van de Waal’s forces A collective term for the weakest
attractions between molecules or atoms. Two major Van
de Waal’s forces are London dispersion forces and
dipole–dipole interactions.vaporization The conversion of a liquid to a gas.vapour Gas; commonly used to mean a gas above a liquid.
Sometimes defined as a gas below its critical temperature.vapour pressure The pressure of a vapour in equilibrium
with a liquid.wavelength The length of a single wave of light of a par-
ticular frequency.wavenumber (cm^1 ) The number of wavelengths of light
per centimetre.weak acids–weak bases Acids or bases that are incom-
pletely ionized in solution.0230_000118_30_Gloss.qxd 3/2/06 2:24 pm Page 457