compensation effect
In a considerable number of cases plots of \(T\ \Delta ^{\ddagger }S\) vs. \(\Delta ^{\ddagger}H\), for a series of reactions, e.g. for a reaction in a range of different solvents, are straight lines of approximately unit slope. Therefore, the terms \(\Delta ^{\ddagger}H\) and \(T\ \Delta ^{\ddagger }S\) in the expression partially compensate, and \[\Delta ^{\ddagger}G = \Delta ^{\ddagger}H - T\ \Delta ^{\ddagger}S\] often is a much simpler function of solvent (or other) variation than \(\Delta ^{\ddagger}H\) or \(T\ \Delta ^{\ddagger }S\) separately.
See also:
isokinetic relationship
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1098 [Terms] [Paper]