Thermodynamic relations for the noncalorimetrical determination of the heat of adsorption in multicomponent systems

The molar heat of adsorption, Δh ad , of a single solute in ideal dilute solution can be determined indirectly from the temperature dependence of the adsorption isotherm by means of the so-called Clausius-Clapeyron equation. The present paper deals with the generalization of this equation to systems with several adsorbing components. The generalization must allow for the nonstoichiometry of the adsorption process; that is for the fact that, in general, the amounts of the adsorbing substances exchanged between the bulk phase and the surface phase are not coupled by constant ratios. Instead, these ratios change with the composition of the bulk solution. These changes can be represented by a path P in the space of the bulk solute concentrations