Surface Thermodynamic Quantities for a Pure Substance

The total free energy of the system is then made up of the molar free energy times the total number of moles of the liquid plus G, the surface free energy per unit area, times the total surface area. Thus 

Because this process is a reversible one, the heat associated with it gives the surface entropy 

Finally, the total surface enthalpy per square centimeter is 

and as a good approximation, and the surface energy are not distinguished, so Eq. III-6 can be seen in the form 

The total surface energy generally is larger than the surface free energy. It is frequently the more informative of the two quantities, or at least it is more easily related to molecular models. 

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