Absolute Rates of Heterogeneous Gas Reactions

Abstract

FOR a decomposition reaction catalysed by a surface, in which the catalysis depends upon the formation of an adsorption complex (in adsorption equilibrium with the gas phase) and subsequent thermal activation and break-up of the complex into new molecular species which then evaporate, simple analogy with the theory of homogeneous reactions leads to an expression for the rate: K = f.n.e^E/RT, where K is the number of molecules reacting per sq. cm. per second, n is the number adsorbed per sq. cm., f is frequency with which an adsorption complex undergoes a change in its total energy content (analogous to collision frequency for a homogeneous reaction), and e^E/RT is an approximate expression for the chance that after any particular energy change the complex is left with energy exceeding E. E is a quantity specific for the complex and not merely for the reaction.