Thermodynamically consistent equations for the accurate description of the logarithm of the solvent activity and related properties of electrolyte solutions with a unique set of parameters. Critical analysis of the mean activity coefficient evaluation

Abstract

Thermodynamically consistent equations for the accurate description of the dependence on concentration of the properties of electrolyte solutions are proposed, based on a polynomial of order i/4 and a unique set of adjustable coefficients. The equation for the logarithm of the solvent activity ln a1(m) was derived first, followed by analogous expressions for the osmotic coefficient ϕ(m), the solvent activity a1(m) and activity coefficient γ1(m) and finally for the mean ionic activity coefficient γo±(m). The descriptive capability of these equations was verified and favorably compares with the extended Pitzer equation. Finally, it was demonstrated that the evaluation of lnγo±(m) is strongly influenced by the fitting capability of the expression used in the correlation of ϕ(m) in the low molality region.