title: Time evolution of the activation energy in a batch chemical oscillator.
abstract: The batch-operated bromate/phosphate/acetone/dual catalyst system was studied at four temperatures between 5 and 35 degrees C. The dynamics was simultaneously followed by potential measurements with platinum and bromide selective electrodes, and spectroscopically at two different wavelengths. By simultaneously recording these four time series it was possible to characterize the dynamics of the sequential oscillations that evolve in time. The existence of three sequential oscillatory patterns at each temperature allowed estimating the activation energies in each case. Along with the activation energy of the induction period, it was possible to trace the time evolution of the overall activation energy at four different stages as the reaction proceeds. The study was carried out for two different sets of initial concentrations and it was observed that the overall activation energy increases as reactants turn into products. This finding was propounded as a result of the decrease in the driving force, or the system's affinity, of the catalytic oxidative bromination of acetone with acidic bromate, as the closed system evolves toward the thermodynamic equilibrium.
authors.affiliation: Instituto de Quiímica de São Carlos, Universidade de São Paulo, C.P. 780, CEP 13560-970, São Carlos-SP, Brazil.
authors.forename: Paulo A
authors.initials: PA
authors.lastname: Nogueira
authors.forename: Hyrla C L
authors.initials: HC
authors.lastname: Oliveira
authors.forename: Hamilton
authors.initials: H
authors.lastname: Varela