Entropy of activation

The entropy of activation is one of the two parameters typically obtained from the temperature dependence of a reaction rate, when these data are analysed using the Eyring equation. Symbolized ΔS^‡, the entropy of activation provides clues about the molecularity of the rate determining step in a reaction, i.e. whether the reactants are bonded to each other, or not. Positive values suggest that entropy increases upon achieving the transition state, which often indicates a dissociative mechanism. Negative values for ΔS^‡ indicate that entropy decreases upon achieving the transition state, which often indicates an associative mechanism. Values near zero are difficult to interpret.^[1]

References

1. ↑ J. H. Espenson Chemical Kinetics and Reaction Mechanisms McGraw-Hill, 1981, ISBN 0-07-019667-2.