Heat production in steady states and oscillations

Measurements were made of the rate of heat production in three oscillatory systems: benzaldehyde oxidation, the Briggs-Rauscher reaction, and the Belousov-Zhabotinsky reaction. In cases where a stable steady state coexists with a limit cycle oscillation or where the steady state undergoes a hard loss of stability to oscillations, the heat production in the oscillatory state was quite different from that of the steady state, varying from 50% less to 210% greater. Bifurcations to oscillations involving a soft loss of stability showed no discontinuity in the heat production, as expected. Consideration of the thermodynamics of these reactions indicates that the contribution to the rate of entropy production due to enthalpy changes dominates that due to differences in the entropies of the products and reactants. In the benzaldehyde oxidation, the changes in heat production are due to a change in the average rate of the reaction, and not due to a change in the distribution of products.