Caloric behaviour in the induction period of Belousov- Zhabotinskii reactions monitored by heat exchange calorimetry of batch type and the simultaneous estimation of the potentiometric aspect

Abstract

The induction period of the Belousov-Zhabotinskii (B-Z) reactions which occur in an aqueous solution composed of potassium bromate, sulphuric acid, malonic acid and ammonium cerium(IV) sulphate was studied in the same reaction by heat exchange calorimetry of batch type and potentiometry. The sample and reference vessels were fixed differentially in a home-made heat exchange calorimeter in a temperature-controlled water bath. The heat evolved in the vessel was exchanged freely with the surrounding water. The rate of heat evolution q and the total heat effect Q were estimated by the analogue treatments of electrical signals observed as temperature changes via thermistors placed in each vessel. A standard potentiometric cell was also present in the water bath in order to obtain simultaneously the potential difference E which reflects the bromide concentration in the reaction. When fine crystals of the cerium(IV) salt are added to start the B-Z reaction, a small endothermic peak is observed in the q versus t curve, followed by large exothermic double peaks. In the induction period, only the smaller change is observed in the potentiometry. The Q values in the induction period depend significantly upon the initial concentrations of KBrO 3 and H 2SO 4 in the solution, in contrast to those of malonic acid and cerium(IV) salt. Several minor fluctuations in Q and the E versus t curves are observed in the induction period of dilute KBrO 3 or H 2SO 4 solution. The Δ H values in the induction period were also estimated in several different concentrations of the initial constitutents.