2.3. The cycle of three reversible first-order reactions In the Laplace domain, defining the symbols
the transformed concentrations AA, BA and AB are given by
and the ratio of the latter two, by
where the Onsager relationship k+1 k+2 k+3 ¼k_1 k_2 k_3 was used in the final step. Hence for all s, LBA (s) and LAB(s) are in fixed proportion given by the equilibrium constant (k+1 /k_1 ). Since the inverse Laplace transform is linear, the same proportion holds in the time domain:
As an example, we show in Fig.1 the time dependence of BA/AA, BB/AB and the time-invariant ratio BA/AB, for the case of isomerization of butenes in Wei and Prater(1962,Eq.(129)):