The concept of ionic hydration has been used earlier to get a new representation of the excess free energy of aqueous, single-electrolyte solutions, which leads to the prediction of y* and # values using only two parameters for each electrolyte at 25ยฐC. Here this concept is extended to cover higher temperatures (up to 300ยฐC) using temperature-dependent parameters. The resulting equations arc tested with experimental data for several electrolytes of different charge types, covering temperatures up to 300ยฐC and concentrations up to an ionic strength of 15 mol kg-l. It is found that six or seven parameters are enough to get excellent predictive accuracy for y* and # over these concentration and temperature ranges. A detailed comparison with equations of earlier works clearly brings out the predictive superiority of the present method. In recent years, one of the earlier approaches, based on a virial equation for excess free energy, has been shown to give comparable predictive accuracy. However, it has been demqnstrated only for a few electrolytes, and involves 15 or more parameters. The genera1 applicability of the present method is therefore obvious. It has also been shown to be useful in the accurate calculation of the thermal properties, such as enthalpy and heat capacity, which involve successive differentiation of the excess free energy with temperature.