More on Arrhenius plots

The meaning and explanation of the Meyer-Neldel rule were long considered to be a mystery, but work by a number of groups in the final decades of the past millennium provided a clear theoretical framework for both kinetic and equilibrium systems. The key to activation is not the energy or enthalpy; it is the free-energy change, which includes an entropy term. When the activation barrier is large, the entropy change increases with Ea, and that increases A. In 2006 one of us (Yelon) coauthored a review of the state of the art in experiment and theory, which have continued to evolve since. Systematic studies yield information concerning the characteristic energy of the collective excitations-phonons or local vibrations -that are aggregated to surmount the activation barrier.