A NEW EQUATION OF STATE FOR CORRELATION AND PREDICTION OF STANDARD MOLAL THERMODYNAMIC PROPERTIES OF AQUEOUS SPECIES AT HIGH TEMPERATURES AND PRESSURES

Abstract

A new expression for partial molar volumes of aqueous solutes at infinite dilution has been developed in an empirical form based on Fluctuation Solution Theory for use over wide ranges of temperature and pressure. The solvent density and compressibility characterize the solvent properties, providing a much better description, especially in the critical region, than do models based on the solvent dielectric constant. The formulation has been integrated and differentiated to obtain analytic expressions for the Gibbs energy of hydration and Henry's constant, as well as the infinite dilution partial molar enthalpy and heat capacity of hydration at supercritical temperatures. For partial molar heat capacities at subcritical temperatures, an additional temperature-dependent function is used. Using newly established comprehensive databases of experimental V20 and C0p,2 for nonelectrolytes and 1-1 electrolytes, supplemented with smaller databases for ΔhydH20 and Δhyd G20 for nonelectrolytes and κ20 for electrolytes, it is shown that accurate correlations of all available data are obtained with the new model. For nonelectrolytes, the accuracy of predictions for all hydration and derivative properties at densities greater than 250 kg m−3 and at temperatures from ambient to over 700 K using only data at 298 K is almost as good as fitting the model's five parameters to all the data. For 1-1 electrolytes, predictions of C0p,2 near the critical temperature from V20 near the critical temperature are satisfactory for NaCl(aq).