Temperature Dependence of the Parameters in the Pitzer Equations

The effects of temperature on the virial coefficients in the Pitzer equations are not known in general, and this is because the vast majority of experiments performed to investigate the properties of the aqueous electrolytes were conducted only at a temperature of 25 °C. Consequently, most of the parameters in the Pitzer equations that are available in the literature were estimated at this temperature. Therefore, finding a way to estimate the virial coefficients at different temperatures is highly important. To achieve this, new equations that correlate the virial coefficients with the temperature and the properties of the ions, i.e., ionic radius and ionic charge, are derived. As a result, these new derived equations were able to accurately predict the apparent relative molal enthalpies at 25 °C, as well as the activity and osmotic coefficients at temperatures up to 150 °C for electrolytes that are unlikely to form ion pairs. Moreover, comparison plots are presented to demonstrate the good agreement between the predictions of the correlating equations and the experimental data obtained from the literature.