Surface Energy and Heat of Vaporization of Liquids

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Abstract
An approximate calculation of the total surface energy of nonpolar liquids is made, by using forces obtained from quantum theory. The formula obtained is somewhat different from that previously used by Margenau, and it is suggested that his calculation gives either the free surface energy, or some closely related quantity. The calculations are made by assuming both that the positions of the molecules obey the simple Maxwell-Boltzmann distribution law appropriate to a dilute gas, and that the distribution is uniform outside of the excluded regions caused by the (approximate) impenetrability of the molecules. For argon, neon, nitrogen, and oxygen the experimental values lie between those computed on these two extreme assumptions; for helium the calculated value is too great, even when uniform distribution is assumed, due probably to the importance of zero-point energy for liquid helium. The heat of vaporization has been calculated in a similar way and for it also the experimental values lie between those based on the two different distributions, except for helium, where the zero-point energy shows up still more prominently, as would be expected.

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