When the activation energy is varied in the first instance, we may observe a related change in pre-exponential factors. An increase in A tends to compensate for an increase in E a,i, which is why we call this phenomenon a compensation effect. Similarly, for the second and third instances, in accordance with the Gibbs free energy equation, with which we derive the listed equations, Δ H scales proportionately with Δ S. The enthalpy and entropy compensate for each other because of their opposite algebraic signs in the Gibbs equation.