Thermodynamic Quantities of Surface Formation of Aqueous Electrolyte Solutions

The surface tensions of aqueous solutions of sodium, magnesium, and lanthanum chlorides were measured as a function of concentration and temperature. By analyzing the results, the concentration dependence of the thermodynamic quantities of surface formation such as entropy (Deltas), Helmholtz free energy (Deltaf), and energy of surface formation (Deltau) were evaluated. The Deltaf increased almost linearly with increasing concentration, and the degree of the increase is mainly determined by the net charges of the salts. The Deltas decreased with the addition of salt into the solution. It was found that the net charge of salts determines the degree of the decrease in Deltas. On the other hand, a slight change in the Deltau is observed because of the opposite contribution of Deltaf and TDeltas to the Deltau value. Copyright 1999 Academic Press.