Surface entropy and energy

The entropy of a system at constant pressure, surface area and composition is  

For a pure liquid the surface entropy per unit area S is  

The total energy per unit area for a pure liquid E is  

It is the work which must be done in order to remove from the bulk of the liquid and bring to the surface a sufficient number of molecules to form a surface unit. Conversely, energy is liberated when a surface disappears due to the return of molecules from the surface to the center of the liquid. The total surface energy of a pure liquid is generally larger than the surface free energy. 

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