If the external stimulus of a catalytic surface imposes a linear response in the binding energy of the surface adsorbates, then potential dynamic catalysis scenarios can be depicted in the right panel of Figure . As shown, the binding enthalpies of A* and B* are related by a line with slope, gamma γ B-A . It is important to note that gamma is defined, and consideration of the reaction in reverse will produce a gamma of inverse value. The point of common surface energy, delta δ, exists for the enthalpy of adsorption of B offset by the heat of reaction. More complicated relationships (i.e., nonlinear) between the surface energies of intermediate species require more than two variables, depending on the applied model.