Role of the Reagents Consumption in the Chaotic Dynamics of the Belousov-Zhabotinsky Oscillator in Closed Unstirred Reactors

Chemical oscillations generated by the Belousov–Zhabotinsky reaction in batch unstirred
reactors, show a characteristic chaotic transient in their dynamical regime, which is generally
found between two periodic regions. Chemical chaos starts and finishes by following a direct and
an inverse Ruelle–Takens–Newhouse scenario, respectively. In previous works we showed, both
experimentally and theoretically, that the complex oscillations are generated by the coupling
among the nonlinear kinetics and the transport phenomena, the latter due to concentration and
density gradients. In particular, convection was found to play a fundamental role. In this paper,
we develop a reaction–diffusion–convection model to explore the influence of the reagents
consumption (BrO
3 in particular) in the inverse transition from chaos to periodicity.
We demonstrated that, on the route towards thermodynamic equilibrium, the reagents
concentration directly modulates the strength of the coupling between chemical kinetics and
mass transport phenomena. An effective sequential decoupling (reaction–diffusion–convection -
reaction–diffusion - reaction) takes place upon the reagents consumption and this is at the basis
of the transition from chaos to periodicity.