The Tammann–Tait–Gibson model. Application to the heat capacities of aqueous electrolyte solutions

Abstract

The Tammann–Tait–Gibson (TTG) model is used to derive a set of equations for the heat capacities of aqueous electrolyte solutions. The parameters of these equations are related to the intrinsic properties of the solute. The limiting partial molal heat capacity, c–op, is made up of three terms. The first is positive and proportional to the heat capacity of the solid. The second is negative and proportional to the TTG molal volume of the solid. The third is also negative and represents the compressional effect of the solute on water. The values of c–op can be predicted directly, without need to extrapolate at very low concentrations. The equations are shown to give good estimates of the heat capacities of arrange of electrolytes (uni- and multi-valent halides, bicarbonates and sulphates). The effects of changes in temperature and pressure and the number of components are considered and a general equation derived to cover these changes. Application to seawater of concentrations up to 130%[≈ 3 mol (kg water)–1] has shown that the heat capacity can be predicted from binary solution data to better than 0.001 cal K–1 g–1, which is less than the experimental errors.