Coupling between nucleation and chemical reactions and its importance in understanding the oxidation of iodine by hydrogen peroxide

Abstract

A physicochemical model of iodine oxidation with hydrogen peroxide is extended by heterogeneous processes, conceptually improving the understanding of the reaction mechanism.

Changing the paradigm in modelling the Bray–Liebhafsky oscillatory chemical reaction

“…In this group of reactions, the last two represent summary reactions of the oxidation of the iodine radical I by H 2 O 2 and H 2 O Ã 2 to iodate. As it is presented earlier, 23 this may be considered a chain radical reaction whose rate-limiting step is the first oneelectron oxidation of I to HIO accompanied by reduction of peroxide to HO . As both products appear at the same reaction place, HO radical need not diffuse from the bulk solution and may (as it is assumed) immediately further oxidize HIO (due to its extremely high standard reduction potential E2.5 V) to IO .…”

“…The basic property of ( 7) is that variation of oxygen concentration within a few percent of the nucleation limit, J may change by many orders of magnitude. Even with such large approximations, the given equations qualitatively describe iodine oxidation (2) alone 23 and may serve as a conceptual base for modeling the whole oscillatory dynamics represented by the summary reactions (1) and ( 2).…”

“…We intend to show that the previous concepts, introduced to simulate step-wise iodine oxidation, 23 For understanding the whole idea and the details of the model itself, we believe that it will be helpful to follow the first brief discussion of each group, given after the model.…”

“…Although as explained earlier, reactions (R17) and (R18) may describe the path of surmounting the large thermodynamic barrier for (2), the crucial steps for the stepwise iodine oxidation 23 are given by processes (R19) and (R20). The process of nucleation (R19), despite the deceptively simple rate, has a rather complex mathematical structure seen in eqn ( 4), (7) and (8).…”

“…Based on all the mentioned results, we numerically simulated stepwise iodine oxidation (2). 23 In this work, we further extended simulations to the whole oscillatory BL reaction based on Bowers representation of the kinetics of nucleation, 24,25 fast collapse of unstable nuclei (existing on energetic maximum), and its energetic coupling with chemical reactions. The obtained results should change the existing paradigm of the BL reaction that the reaction mechanism may be completely understood as a homogeneous system and described only with mass-action kinetics.…”