Partial molar enthalpies in the NaCl + CaCl2+ H2O system. Application of the McKay–Perring method to thermal measurements

Abstract

The partial molar enthalpy of water at 298 K is determined over a wide range of composition in the NaCl + CaCl₂+ H₂O system and the application of the McKay–Perring treatment to thermal measurements is examined. Unlike the water activity, which necessarily diminishes upon adding salts, the partial enthalpy of water can be of either sign in different parts of the phase diagram, thus ruling out the general use of comparisons at a fixed value of the partial molar enthalpy of water and necessitating the alternative approach through a fixed molality function. The resulting partial enthalpies of NaCl and CaCl₂ are naturally less precise than the experimental H₂O values from which they are derived.