MODEL OF THERMODYNAMIC PROPERTIES OF ELECTROLYTIC AQUEOUS SOLUTIONS

A new chemical-physical group contribution model for activity coefficient is proposed to estimate the equilibrium properties of aqueous solutions containing electrolytes. The chemical part of the model accounts for the hydration equilibrium of water and ions with the formation of ions n-water complexes in a single stage process; n, the hydration number, and K, the hydration equilibrium constant, are the two independent parameters in this part. The physical part of the model is the UNIFAC group-contribution model for short range interactions. Each ion is considered as a group. Long range interactions are accounted for by a Pitzer (Debye and Huckel theory) contribution. The model is compared to experimental data including water activity, osmotic coefficients, activity coefficients, and pH etc. of binary concentrated electrolyte solutions (20M NaOH, 16M HCl, etc.).