Thermodynamic quantities of surface formation of aqueous electrolyte solutions -: I.: Aqueous solutions of NaCl, MgCl2, and LaCl3

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 (Delta s), Helmholtz free energy (Delta f), and energy of surface formation (Delta u) were evaluated. The Delta f increased almost linearly with increasing concentration, and the degree of the increase is mainly determined by the net charges of the salts. The hs 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 hs. On the other hand, a slight change in the Delta u is observed because of the opposite contribution of Delta f and T Delta s to the Delta u value. (C) 1999 Academic Press.