A substance that increases the rate of a reaction without modifying the overall standard
Gibbs energy change in the reaction; the process is called
catalysis. The catalyst is both a
reactant and
product of the reaction. The words catalyst and
catalysis should not be used when the added substance reduces the
rate of reaction (see
inhibitor ).
Catalysis can be classified as
homogeneous catalysis, in which only one phase is involved, and
heterogeneous catalysis, in which the reaction occurs at or near an
interface between phases.
Catalysis brought about by one of the products of a reaction is called autocatalysis.
Catalysis brought about by a group on a reactant molecule itself is called
intramolecular catalysis. The term
catalysis is also often used when the substance is consumed in the reaction (for example: base-catalysed
hydrolysis of
esters). Strictly, such a substance should be called an
activator.
See also: autocatalytic reaction,
bifunctional catalysis,
catalytic coefficient,
electron-transfer catalysis,
general acid catalysis,
general base catalysis,
intramolecular catalysis,
micellar catalysis,
Michaelis-Menten kinetics,
phase-transfer catalysis,
pseudo-catalysis,
rate of reaction,
specific catalysis
Source:
PAC, 1996, 68, 155
(Glossary of terms used in chemical kinetics, including reaction dynamics.)
