3742
J. Phys. Chem. A 2010, 114, 3742
Reply to the “Comment on ‘Mechanistic Investigations on the Belousov-Zhabotinsky Reaction with Oxalic Acid Substrate. 2. Measuring and Modeling the Oxalic Acid-Bromine Chain Reaction and Simulating the Complete Oscillatory System’” Maria Wittmann* and Zolta´n Noszticzius Center for Complex and Nonlinear Systems and the Department of Physics, Budapest UniVersity of Technology and Economics, H-1521 Budapest, Hungary ReceiVed: January 20, 2010 P. Machado and R. Faria1 found a problem regarding a reaction appearing in our paper on the Belousov-Zhabotinsky (BZ) reaction with oxalic acid substrate.2 In our first paper on the BZ reaction with oxalic acid substrate,3 we studied the reaction between oxalic acid and acidic bromate, called reaction R.V
Η+ + ΒrΟ3- + (CΟΟΗ)2 f ΗΒrΟ2 + 2CΟ2 + Η2Ο (R.V) We found a bilinear dependence of the reaction rate on the bromate and the oxalic acid concentrations that can be described by the following rate law:
rV ) kV[ΒrΟ3-][(CΟΟΗ)2] kV was found to be 7.47 × 10-4 M-1 s-1, in good agreement with the data of Sˇevcˇik et al.4 kV depends on the hydrogen ion concentration. The above value is valid in a 1 M sulfuric acid solution.
In the Introduction of our first paper3 (reactions R.I, R.III, and R.V) we suggested that the mechanism of the oxidation of oxalic acid by oxybromine species is an oxygen atom transfer from a molecular oxybromine species to the oxalic acid. Thus (R.V) was written in an alternate form:
(CΟΟΗ)2 + ΗΒrΟ3 f 2CΟ2 + Η2Ο + ΗΒrΟ2 (R.V*) assuming that the active species in this reaction is bromic acid, which occurs probably in a very low concentration in the acidic bromate solution. This hypothesis is supported by the fact that in a neutral solution the reaction rate is practically zero. We have not studied, however, the pH dependence of the rate of the overall reaction, so in all our calculations we used always (rv) with kV ) 7.47 × 10-4 M-1 s-1 because the medium was always 1 M sulfuric acid. These two alternative forms, (R.V) and (R.V*), lead to the misunderstanding especially because in our second paper on the BZ reaction with oxalic acid substrate2 we wrote (R.V*) instead of the more appropriate (R.V) when the reactions were listed in Table 1. The numerical simulations in our second paper were obtained with the rate law (rv); thus bromic acid does not play an explicit role in our model. References and Notes (1) Machado, P.; Faria, R. J. Phys. Chem. A, DOI: 10.1021/jp911520f. (2) Pelle, K.; Wittmann, M.; Lovrics, K.; Noszticzius, Z. J. Phys. Chem. A 2004, 108, 7554. (3) Pelle, K.; Wittmann, M.; Lovrics, K.; Noszticzius, Z.; Turco Liveri, M. L.; Lombardo, R. J. Phys. Chem. A 2004, 108, 5377. (4) Sˇevcˇik, P.; Adamcˇikova´, L.; Guna´rova´, D.; Kovacˇikova´, D. Acta Fac. Rerum Nat. Comenianae (Chimica) 1983, 31, 17.
JP100570K
10.1021/jp100570k 2010 American Chemical Society Published on Web 02/12/2010
