This isotherm takes into account indirect adsorbate–adsorbate interactions on adsorption isotherms. Temkin noted experimentally that heats of adsorption would more often decrease than increase with increasing coverage.
The heat of adsorption ΔH is defined as
He derived a model assuming that as the surface is loaded up with adsorbate, the heat of adsorption of all the molecules in the layer would decrease linearly with coverage due to adsorbate–adsorbate interactions:
where α is a fitting parameter. Assuming the Langmuir adsorption isotherm still applied to the adsorbed layer,  is expected to vary with coverage as follows:
Langmuir's isotherm can be rearranged to
Substituting the expression of the equilibrium constant and taking the natural logarithm: