Coupling of free energies in the formation of intermediates during the catalytic decomposition of H₂O₂

The kinetic and thermodynamic aspects of a two-intermediate scheme proposed previously to describe the catalytic decomposition of H₂O₂ by iron(III)-based catalysts have been investigated. Under non-stationary conditions there is a partial transfer of free energy liberated in the decomposition of H₂O₂ to assist the formation of the secondary intermediate, C_II. The accumulation of C_II can be driven, for a limited period of time, against a free-energy gradient in respect of the initial reactants (the free catalyst E and H₂O₂). The kinetic condition for coupling is the reversal of sign of the net rate of formation of the precursor of C_II (C_I) from E and H₂O₂. Kinetic and thermodynamic aspects of the occurrence of coupling between an endergonic and an exergonic process are discussed in the general case.