Measurement of enthalpies and heat capacities of activation by differential methods

Abstract

A differential method of measuring small differences in reaction rate is described and applied using a double-beam spectrophotometer for the iodination of acetone and a conductivity bridge for the solvolysis of t-butyl chloride. An accurate comparison of reaction rates measured at two temperatures a few degrees apart differentiates the Arrhenius equation and allows the variation of ΔH^≠ and ΔS^≠ with T to be measured. The data for t-butyl chloride is interpreted in terms of a hypothetical ion-pair mechanism.