High-temperature thermodynamic properties of aqueous sodium sulfate solutions

A flow calorimeter has been used to measure the heat capacities of aqueous sodium sulfate solutions from 30°C to 200°C at 1 bar, or the saturated vapor pressure, and at 200 bar.The heat capacity data have been integrated as a function of temp~rature to obtain values of the apparent molal enthalpy, osmotic coef~icient, and mean activity coefficient.Osmotic coefficients obtained in this manner are in good agreement with available literature data over the entire temperature range.These results indicate that heat capacity measurements can be used reliably to obtain the high temperature activity properties of ,electrolyte solutions, provided the enthalpy and Gibbs energy are known at 25°C.