https://doi.org/10.1351/goldbook.L03551
A linear correlation between the logarithm of a
rate constant
or
equilibrium constant
for one series of reactions and the logarithm of the
rate constant
or
equilibrium constant
for a related series of reactions. Typical examples of such relations (also known as linear Gibbs energy relations) are the
Brønsted relation
, and the
Hammett equation
.
The name arises because the logarithm of an
equilibrium constant
(at constant temperature and pressure) is proportional to a standard
free energy
(Gibbs energy) change, and the logarithm of a
rate constant
is a linear function of the
free energy
(Gibbs energy) of
activation
.
It has been suggested that this name should be replaced by linear Gibbs energy relation, but at present there is little sign of acceptance of this change. The area of physical organic chemistry which deals with such relations is commonly referred to as 'Linear Free-Energy Relationships'.
See also:
σ-constant
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1136 [Terms] [Paper]