Consider a liquid of density ρ with molar mass M. Explain why the number of molecules per unit area in the surface is approximately
(ρNA/M)2/3.
Hence, the energy contribution per molecule to the surface tension γ is approximately
γ/(ρNA/M)2/3.
Evaluate this quantity for water (surface tension at 20∘C is approximately 72mJm−2) and express your answer in eV. Compare your result with the latent heat per molecule (the molar latent heat of water is 4.4×104Jmol−1).