Fluctuation thermodynamic properties of reactive components from species correlation function integrals

Abstract

Completely general expressions are given for the equilibrium composition fluctuation properties of systems of components that can undergo reactions (dissociation, association, ionization, solvation) to form new species. Concentration derivatives of the component chemical potentials obtained for non-reacting systems by Kirkwood and Buff are expressed for reacting systems in terms of integrals of the total correlation functions and of the direct correlation functions between the species. This formalism leads to rigorous expressions necessary for modelling fluctuation properties in electrolyte solutions, and in solution theories such as the chemical theory and the solution of groups method for activity coefficients. It is shown that the total correlation function integrals implicitly contain the long range effects of the reactions, but that the direct correlation function integrals (DCFI) do not. Rather, the projection operators for the species DCFI contain the reaction thermodynamics explicitly.