Apparent Activation Energy and Frequency Factor for a Process Involving Competing Mechanisms

Abstract

If a process involves competing mechanisms, each of which individually obeys Arrhenius' equation, the dependence of the combined rate on temperature is in general not of this type. However, apparent activation energies and frequency factors can be measured. In this paper, several sets of mechanisms distributed with respect to activation energy are considered and the apparent activation energies and frequency factors are calculated in terms of the parameters of the distributions. The results for a two-peak distribution, a flat distribution, and a truncated exponential distribution are given analytically and graphically. A simple approximate method is described for determining the apparent activation energy in some cases. Some remarks are made about the ``compensation effect.''