Isoteric heats and heats of adsorption for constant change of interfacial tension were obtained for the adsorption of 1, 2, 3, 4, 5, 6-hexachlorocyclohexane on inorganic and organic materials. The latter quantity, ΔHφ, was shown to represent the true difference between the adsorbed solute and the solute in solution in partial molar enthalpy at equilibrium. Values of ΔHφ were calculated from the equation δHθ= RT1T2 T2-T1ln (m23 m2)T2 (m23 m2)T1 derived for dilute solutions with the assumption that Henry's law applies and the properties of the surface remain unchanged by adsorption. From changes in ΔHφ it was possible to conclude that the site energies are of wide range on the inorganic surfaces studied but of relatively narrow range on the organic fractions of the adsorbents for the range of surface coverage studied. Both the partial molar enthalpy, ΔH′, and entropy, ΔS′, corrected for the temperature-solubility effect of the solute were obtained. Values of ΔS′ increased uniformly with surface coverage, which is to be expected if there is a range of energy sites and the degrees of freedom increase with surface coverage. It appears that the configurational entropy of the beta-isomer adsorbed from water on bentonite is quite high; the lowest ΔS′ values were obtained for the adsorption of γ- and β-isomers from water on silica gel. © 1969.
