A new equation of state for correlation and prediction of standard molal thermodynamic properties of aqueous species at high temperatures and pressures

A new expression for partial molar volumes of aqueous solutes at infinite d ilution has been developed in an empirical form based on Fluctuation Soluti on 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 mode ls based on the solvent dielectric constant. The formulation has been integ rated and differentiated to obtain analytic expressions for the Gibbs energ y of hydration and Henry's constant, as well as the infinite dilution parti al molar enthalpy and heat capacity of hydration at supercritical temperatu res. For partial molar heat capacities at subcritical temperatures, an addi tional temperature-dependent function is used. Using newly established comp rehensive databases of experimental V-2(0) and C-p.2(0) for nonelectrolytes and 1-1 electrolytes, supplemented with smaller databases for Delta(hyd) H -2(0) and Delta(hyd) G(2)(0) for nonelectrolytes and KO for electrolytes, i t is shown that accurate correlations of all available data are obtained wi th 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 C-p,2(0) near the critical temperature fro m V-2(0) near the critical temperature are satisfactory for NaCl(aq). (C) 2 000 Elsevier Science B.V. All rights reserved.