Thermodynamic properties of solutions of a hydrolyzing electrolyte: relative partial molar enthalpies and heat capacities, solvent activities, osmotic coefficients, and solute activity coefficients of aqueous sodium carbonate

Abstract

For solutions of Na 2CO 3 and other hydrolyzed solutes, a complete treatment of the thermodynamic properties must include the contributions from hydrolysis in addition to those from interionic and related effects. The hydrolysis contributions can become very large at low molalities. This paper presents a coherent treatment of the relations among the thermodynamic properties and includes the hydrolysis contributions in a straightforward manner without approximations. The treatment distinguishes between the equilibrium-state properties and the conventional properties attributed to constituents and related to Debye-Hückel models. The treatment is outlined in some detail, since it has not appeared previously in the literature. The equations are applied to the available enthalpies, heat capacities, and solvent activities, to evaluate the activity coefficients of Na 2CO 3(aq) up to saturation at 298.15 K by the Gibbs-Duhem equation, and outlines procedures for evaluation at other temperatures. The principles are general and can be adapted to other systems of this type.