Procedure for the calculation of the Gibbs energies of hydration for volatile solutes from solubility data.

J. ALVAREZ Y R. FERNÁNDEZ PRINI

Boulder, USA

Workshop; Sixteenth Symposium of Thermophysical Properties; 2006

National Institute of Standards and Technology

The determination of the Gibbs energy of hydration (DhydG2¥) of volatile nonpolar solutes is frequently accomplished through Herny’s constant (kH) which in turn, for gaseous solutes, is calculated with the solublity of the solutes. The solubility of nonpolar or slightly polar simple gases in water under ambient conditions and liquid-vapor coexistence has been determined experimentally with extreme precision. However when the solvent’s vapour pressure is appreciable corrections for nonideality have to be taken into account and they become increasingly important as the critical temperature of water is approached. In order to obtain DhydG2¥ at high temperatures, the experimentally measured solubility has to be processed by careful iterations that require the use of equations for model systems.  We have employed a perturbation method to express the chemical potential of the solute and the corresponding equations for the partial molar volume at infinite dilution and the activity coefficient of a hard-sphere equivalent solute. The different steps in the complete procedure to calculate DhydG2¥ will be analyzed as well as the uncertainty generated on the final value. If the gaseous solute is relatively soluble in water, e.g. CO2, even under ambient conditions the need to consider nonideality (solute’s activity coefficie