Posted on November 28, 2016 in
The nature of the temperature dependence on reaction rates is reviewed. The Arrhenius equation is discussed with special attention paid to the two key terms: the activation energy Ea, and collision frequency A. While the latter term is usually considered temperature-independent, we examine this assumption in more detail for gas, liquid and solid states. In liquid state, collision frequency is dependent on temperature linearly resulting in an apparent effective additional activation energy of 0.6 kcal/mol. In the solid state, the Arrhenius equation apparent activation energy is again composed of two terms: one related to the barrier for the reaction and another related to the barrier for breaking intermolecular bonding to enable collisions. It is suggested (though not proved) that observed higher activation energies associated with solids compared to solutions may be a result of this higher added activation process for movement in solids.