Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: Standard partial molal properties of organic species

The standard partial molal properties of organic aqueous species at high pressures and temperatures can be predicted using an adaptation of a revised equation of state for inorganic aqueous ions and electrolytes (Tanger and Helgeson, 1988), together with correlations among equation of state parameters (SHOCK and Helgeson, 1988). These correlations include a charge-dependent relation between Born coefficients and the standard partial molal entropies of aqueous species at 25°C and 1 bar (SHOCK. et al., 1989). Thermodynamic calculations indicate that in the liquid phase the standard partial molal volumes (V̄°), heat capacities (C̄°_p), and entropies (S̄°), as well as the apparent standard partial molal enthalpies of formation (ΔH°) of aqueous electrolytes with organic anions maximize with increasing temperature at Psat^* * P_sat represents pressures corresponding to liquid-vapor equilibrium for the system H₂O, except at temperature < 100°C where it refers to the reference pressure of 1 bar. and approach - ∞ at the critical point of H₂O. In contrast, the corresponding properties of neutral organic aqueous species in the liquid phase minimize with increasing temperature Psat and approach ∞ at the critical point of H₂O. Predicted equilibrium constants for alkane solubilities and carboxylic acid dissociation reactions at elevated pressures and temperatures are in close agreement with experimental data reported in the literature, which supports the validity and generality of the equations of state as well as the predictive algorithms used in the calculations. As a consequence, high temperature/ pressure standard partial molal properties, as well as equilibrium constants and other reaction properties, can be predicted for reactions involving a wide variety of organic aqueous species for which little or no experimental data are available at temperatures > 25°C. Present capabilities permit such predictions to be made for hydrothermal and magmatic conditions at pressures and temperatures as high as 5 kb and 1000°C.