In a series of elementary reactions, the changes in Gibbs activation energies are often found to be proportional to the changes in Gibbs energies for the overall reaction.$$\mathrm{\delta }{\mathrm{\Delta }}^{‡}G=\alpha {\mathrm{\Delta }}_{\mathrm{r}}{G}^{\circ }$$ This relation was interpreted in terms of the simple assumption that a small change in any transition-state property $P_{‡}$ is a linear combination of changes in reactant- and product-state properties, $P_{\mathrm{R}}$ and $P_{\mathrm{P}}$. $$\mathrm{\delta }{P}_{‡}=\alpha \mathrm{\delta }{P}_{\mathrm{P}}+(1-\alpha )\mathrm{\delta }{P}_{\mathrm{R}}$$ Within the limits of this assumption, the parameter $\alpha$ is an approximate measure of the fractional displacement of the transition state along the minimum-energy reaction path from reactants to products.