𝐾 𝑖 is the equilibrium constant at step i (i = 1, 2, 4-7). and 𝑘 𝑖 is the rate constant for the forward reaction in step i, 𝑘 -𝑖 is the rate constant for the reverse reaction in step i. Substituting eq. 9 into eq. 10, a model equation for the reaction rate was derived.