where k B = 1.38 × 10 -23 J/K is the Boltzmann constant, T is the absolute temperature, ∆G ‡ XY is the Gibbs free energy barrier for a transition from state X to state Y at a given temperature, ∆G PC is the Gibbs free energy of the reaction step Products → C, and ∆G RA is the Gibbs free energy of the reaction step Reagents → A. This barrier provides an estimate of the rate of an effective reaction Reagents --→ Products with a rate constant given by the Eyring-Polanyi equation: