Application of a Chemical Thermodynamic Model to the Gibbs Free Energy of Aqueous Electrolyte Solutions. New Equations for the Activity and Osmotic Coefficients

Abstract

The chemical thermodynamic (CT) model, based on the extended Tait equation, has been applied to the Gibbs free energy of aqueous solutions of sodium chloride and potassium chloride at 25°C. Equations for the activity and osmotic coefficients were derived. These are made up of the Debye-Huckel limiting slope term, a van der Waals co-volume effect term covering short-range repulsion, a term covering the water compression by the solute and a short-range attractive term. The distance of closest approach derived from the model is the same as that expected for the van der Waals effect. The individual components of the partial molal free energy, that is, the effects of solute concentration on the water and solute respectively, have been calculated.