Isopiestic studies of very concentrated aqueous electrolyte solutions of LiCl, LiBr, LiNO 3, Ca(NO 3) 2, LiNO 3 + KNO 3, LiNO 3 + CsNO 3, and Ca(NO 3) 2 + CsNO 3 at 100 to 150°C

Abstract

Thermodynamic properties of aqueous salt solutions show marked changes when the water content is reduced below 4 to 8 mol of H 2 O per mole of salt, reflecting the gradual transition between aqueous electrolytes and molten salts. The enthalpy of vaporization of water rises from values near that of pure water to values characteristic of water at infinite dilution in molten salts. Water activities at high concentrations have been determined from precise isopiestic measurements of LiCl, LiNO 3 , LiBr, Ca(NO 3 ) 2 and several mixtures including (Li, K)NO 3 at 100 to 150°C. All show a region in which Stokes and Robinson's B.E.T. adsorption model of hydration can be fitted with physically reasonable energy parameters. For the system (Li, K)NO 3 + H 2 O, the difference between the energy of adsorption and energy of liquefaction, calculated with the model, is 0.7 kcal mol −1 , while the difference between the enthalpies of vaporization of water at infinite dilution in salt and of pure water is 0.8 kcal mol −1 .