Prediction of the thermodynamic properties of electrolytes at high pressures and temperatures

The thermodynamic behavior of aqueous electrolytes at high pressures and temperatures can be predicted with the aid of theoretical equations incorporating explicit provision for ion association, solvation, and long- and short-range interaction, the intrinsic properties of aqueous species, and electrostriction collapse of the local solvent structure. Parameters derived from fits of the equations to experimental data at low pressures and temperatures can be used to predict both the standard and relative partial molal properties of aqueous electrolytes at high pressures and temperatures. Calculations of this kind afford estimates of the relative enthalpies, heat capacities, and densities of NaCl solutions at pressures and temperatures to 5 kbar and 600°C. These estimates and the theoretical equations used to calculate them are summarized below, together with predicted activity and osmotic coefficients, apparent standard partial molal Gibbs free energies of formation, and other thermodynamic properties of aqueous electrolytes at high pressures and temperatures.