Infinite dilution partial molar properties of aqueous solutions of nonelectrolytes. II. Equations for the standard thermodynamic functions of hydration of volatile nonelectrolytes over wide ranges of conditions including subcritical temperatures

The volumetric equation proposed previously (Plyasunov et al., 2000), for e stimating the infinite dilution Gibbs energy of hydration of volatile nonel ectrolytes at temperatures exceeding the critical temperature of pure water , T-c, is extended to subcritical temperatures. The basis for the extension without inclusion of new fitting parameters besides the experimental value s of the thermodynamic functions of hydration at 298.15 K, 0.1 MPa, is an a uxiliary function, Delta(h)Cp(0)(T, P-r), for the variation of the infinite dilution partial molar heat capacity of hydration of a solute in Liquid-li ke water between temperatures T = 273.15 K and T = T-s = 658 K along the is obar P-r = 28 MPa. The analytical form of Delta(h)Cp(0)(T, P-r) was found b y globally fitting all available data for the seven best-studied solutes (C H4, CO2, H2S, NH3, Ar, Xe, and C2H4). Four constraints were used to determi ne the values of four terms of the Delta(h)Cp(0)(T, P-r) function: the nume rical values of the temperature increments between T = 298.15 K and T = T-s = 658 K for the Gibbs energy and the enthalpy of hydration, and numerical value of the heat capacity at T-s and at 298.15 K, all at the selected isob ar P-r. This approach, in combination with the volumetric equation, may be used to describe and predict all the infinite dilution thermodynamic functi ons of hydration for nonelectrolytes over extremely wide ranges of temperat ure and pressure. The model allows calculation of the standard state partia l molar properties, including the Gibbs energy of aqueous solutes in a sing le framework for conditions from high-temperature magmatic processes throug h hydrothermal phenomena to low-temperature conditions of hypergenesis. Cop yright (C) 2000 Elsevier Science Ltd.