The adsorption of vapours on mercury. II. The entropy and heat of adsorption of non-polar substances

Abstract

An attempt has been made to interpret the entropy of adsorption of benzene, toluene and n-heptane on mercury. These investigations have indicated with fair accuracy the amount of translational and rotational freedom possessed by the substances on the surface of mercury. The most striking result was obtained with benzene, where by denying all rotation except in the plane of the ring and denying the third degree of translational freedom, the calculated entropy of adsorption agreed closely with the experimental value. The surface mobility of toluene was found to be considerably hindered, and the entropy of adsorption of n-heptane confirmed the view that the molecules were partially rolled up. An attempt has been made to derive the theoretical heat of adsorption of benzene from various relations for the attractive and repulsive potentials for the van der Waals forces near a metal surface. The values obtained were of the same magnitude as the experimental value. The calculations gave some evidence of the ranges of intermolecular distance over which the different equations for the attractive potential were accurate.