It was pointed out that, although this equation had been applied to many solid-state reactions, this habit lacked any theoretical justification because the energy distribution among the immobilized constituents of a crystalline reactant was not described by the Maxwell-Boltzmann equation. The present analysis drew attention to the role which was played by the reactant/profile interface; the active zone within which chemical changes preferentially occurred in many solid-state processes. Interface energy levels which were precursors of the bond redistribution step, were identified as being extensions to the band structure of the solid into the structurally less regular reaction zone. These interface energy levels were analogous to impurity levels. It was noted that electron reorganization required a locally high energy, so the interface levels were appreciably higher than the Fermi level of the crystalline reactant and product. The occupancy was determined by energy distribution functions that were based upon Fermi-Dirac statistics for electrons, and Bose-Einstein statistics for phonons. In the case of the highest energies, that were necessary for reaction, both distributions approached the exponential energy term. This therefore provided some theoretical justification for the application of the Arrhenius equation to the reactions of solids. It was concluded that the results of the present study were most directly relevant to the reactions of ionic solids.

A.K.Galwey, M.E.Brown: Proceedings of the Royal Society A, 1995, 450[1940], 501-12