The unimolecular character of the classical Brunauer, Emmett and Teller adsorption equation and moisture adsorption

A reformulation of the classical Brunauer, Emmett and Teller multimolecular adsorption equation resulted in a unimolecular equation in which a third parameter was introduced into general statements. The third parameter represented adsorption centres on the unimolecular surface. This parameter modified the constant C in the BET equation to C^1/n which, on analysis, was found to measure the density of the most strongly adsorbed molecules. The new equation, which was shown to apply to all isotherm shapes, delineated limits between which three states of unimolecularly adsorbed molecules could be identified along the isotherm. It also provided a new method for calculating the net heat of adsorption, which is identical with the Clausius–Clapeyron equation at low values of Aw. The equation also explained the phenomenon of adsorption compression in sorption studies and this was because of the increased density of primary adsorbate molecules at low values of Aw.