Entropy-Enthalpy Compensation

Synonyms

Compensation temperature; Entropy–enthalpy compensation; Isokinetic temperature; Statistical artifacts

Introduction

Enthalpy–entropy compensation is the concept that differences in the standard enthalpy of reaction ΔH⁰ for different reactions may be compensated for by differences in the standard entropy of reaction ΔS⁰, and that such compensation is so common as to be almost universal. The concept applies equally to kinetic data, variations in the enthalpy of activation ΔH^‡ being compensated for by variations in the entropy of activation ΔS^‡. Thermodynamic data are usually obtained from van ’t Hoff plots and activation data from Arrhenius plots. Calorimetric measurements in principle allow enthalpies and entropies to be measured independently and are less susceptible to some of the difficulties discussed here.

Enthalpy–entropy compensation derives ultimately from an observation almost a century ago of a straight-line relation between the logarithm of the frequency factor and...