ABSTRACT

Experimental values are required of the Gibbs energy as a function of temperature and pressure for the complete thermodynamic characterization of an electrolyte solution and of any solid or vapor phase that is in thermodynamic equilibrium with it. This chapter suggests that solvent mixtures can be easily studied if all but one of the solvents are relatively nonvolatile, e.g., dibutylphthalate or glycerol. The vapor pressure of a solution changes rapidly with temperature due to the large enthalpy of vaporization of the solvent from that solution. The chapter considers the following to be reasonable criteria for deciding whether to use the isopiestic molality ratios to refine a particular pair of isopiestic reference standards. It also consider the use of mercury metal as a heat transfer medium for isopiestic experiments involving electrolyte solutions to cause more problems than benefits, and its use should be avoided.