Thermal behavior of Belousov-Zhabotinskii reactions with Ce(IV) salts measured by heat exchange calorimetry of flow type involving simultaneous observation of potentiometric oscillations

Abstract

Thermal and potentiometric oscillations of Belousov-Zhabotinskii reactions catalyzed by Ce(IV) salt were simultaneously observed in a continuously stirred tank reactor. A heat exchange calorimeter of flow type was assembled. An Ag-AgBr electrode and one end of salt bridge were incorporated in the sample and reference vessels. Three kinds of stock solutions in 0.200 M sulfuric acid were used in typical runs, at concentrations of 0.420 M for potassium bromate, 0.900 M for malonic acid and 3.00 mM for ammonium cerium(IV) sulfate. Each reaction solution was introduced to the sample vessel of 50.86 cm 3 via three flow paths in the range of flow rate from 0.985-21.46 cm 3 min −1 or of residence time τ from 3098 to 142 s. The total heat effect Q and the potential difference of bromide ions E in every oscillation were observed against time t and recorded on a Y− t recorder. Q (in Joules) was monotonously decreased with τ and each oscillation cycle T c of Q and E showed a maximum at τ = 1053 s. The high period of E which corresponded to the heat evolving period was prolonged with decrease in τ. At τ = 144 s, irregular oscillations in cycle were observed. When all the components were concentrated twice, chaotic oscillations were obtained at τ = 1053 s. By changing each concentration of four components to one half and twice, Q and E versus t curves were also observed.