Thermodynamics of the constant-volume principle for chemical processes involving the solvent

Abstract

A comprehensive thermodynamic formalism is developed for applying the constant-volume principle to chemical and transport processes in condensed phases involving the solvent stoichiometrically. These processes comprise simple ionization equilibria in solution and rate processes in the bulk (dielectric relaxation, electrical conductivity, self-diffusion, viscosity etc.) described by the transition-state theory. The formalism is based on special partial molar properties and ideal solutions for studies at constant temperature and molar volume. Isochoric standard molar changes in thermodynamic quantities of reaction, Δ_rX^O_(v)(T, V_m), are introduced in relation to a model process using specific standard states. Real and ideal isochoric conditions leading to intrinsic isochoric conditions for iso-molar-volume processes are established. Relationships between Δ_rX^O_(V)(T, V_m) where X=A, U, S and C_v, and Δ_rM^o(T, p) where M=G, H, S and C_p, respectively, are given and shown to be generally equivalent to the traditional equations. A detailed analysis of the isochoric condition proposed by Williams and of the ensuing controversy is made. The concept of activation pressure is discussed. The concepts of constant volume and activation pressure can both be correctly described in terms of the isochoric model processes and special standard states used in the formulation of intrinsic isochoric conditions.