Application of Gibbs-ensemble methods to reaction kinetics in non-ideal systems

The principle of microscopic reversibility is applied to the transitions between states of an equilibrium Gibbs-type statistical-thermodynamic ensemble in which there is a chemical equilibrium. For simple reactions rates Jf and Jb termed ensemble rates are defined and are shown to be related by Jf/Jb= exp (A/kT), in ideal and non-ideal systems alike, where A denotes reaction affinity for ensemble members whose composition differs significantly from the equilibrium composition. This result is used in conjunction with the contracted stochastic model developed by Widom and the work of Temkin to discuss the relationship between phenomenological forward and backward rates rf and rb for normal reacting systems. It is concluded that the conditions under which rf/rb= exp (A/kT) holds for ideal systems apply equally to non-ideal systems. The theoretical basis of mass-action kinetics is discussed.