We investigated the process of a bromination reaction of malonic acid and methylmalonic acid in the Belousov-Zhabotinsky reaction by using a quartz crystal microbalance (QCM). The process involves an enolization reaction as a rate-determining step. We found that, in the step, the variation of Br 2 concentration induced an exactly quantitative shift of a resonant frequency of the QCM, based on the change of the surface mass on the QCM and the solution viscosity and density. This new finding

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... ed us to estimate the reaction rate constants and the thermodynamic parameters of the enolization reaction due to a QCM measurement. The values measured by the QCM were in good agreement with those measured by a UV-spectrophotometer. As a result, we succeeded to develop a new measurement method of a nonlinear chemical reaction.