The observable consequence of the limitation that the rate of a
bimolecularchemical reaction in a homogeneous medium cannot exceed the rate of
encounter of the reacting
molecular entities. If (hypothetically) a
bimolecular reaction in a homogeneous medium occurred instantaneously when two reactant molecular
entities made an
encounter, the
rate of reaction would be an
encounter-controlled rate, determined solely by rates of
diffusion of reactants. Such a hypothetical '
fully diffusion controlled rate' is also said to correspond to '
total microscopic diffusion control', and represents the asymptotic limit of the
rate of reaction as the
rate constant for the chemical conversion of the
encounter pair into product (or products) becomes large relative to the
rate constant for separation (or
dissociation) of the
encounter pair. '
Partial microscopic diffusion control' is said to operate in a homogeneous reaction when the rates of chemical conversion
and of separation are comparable. (The degree of microscopic
diffusion control cannot usually be determined with any
precision.)
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1140
See also:
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC
Recommendations 1996))
on page 173