Oscillatory reactions in chemical and biological systems are extensively studied1 in various laboratories.'In the iodate-Mn2+ system oscillations in the concentration of iodide have been established.2The mechanistic aspects in the iodate~Mn2+ as well as in the bromate-Mn2+/Ce3+ systems have been studied in our laboratories/14 The present note describes the effect of temperature on the time of oscillations and the determination of the apparent energy of activation of the overall process.The oscillations in the above systems are followed potentiometrically using a platinum electrode and a saturated calomel electrode. All constituents except H202 (The concentration used were KIO;}: 0.06 M, H202: 1.20 M, H2S04: 0.Q5N, MnS04: 0.006 M; CH'2{COOH)2: 0.05 M and starch 0.01%) are kept stirred and thermostated in a polythene beaker. The use of a polythene beaker as the container has been shown3,4 to be essential for obtaining reproducible results. The addition of the requisite amount of H202 triggered the oscillations. The oscillations can he followed either by reading the deflections in the pH meter or the alternate appearance and disappearance of blue color characteristic of the starch-iodine complex. In the present study a x-t recorder was employed to monitor the oscillations. The potential oscillations have been shown3,4 to he arising from the alternating redox reaction in the Mn2+/Mn:i+ couple. Reproducibility of the oscillations was established under a given set of conditions.Temperature is seen to have a profound influence on the total time (f) of the reaction. The time {£) is seen to decrease from 65 min at 0°C to 0.66 min at 61°C. However, the number of oscillations ( 35) remains the same. The apparent rate constant (k) is inversely proportional to t. A plot of log (1/0 against (1/T) yields a straight, line from whose slope the apparent energy of activation for the overall process is found to be 13.70 Kcal. By virtue of its simplicity, reproducibility and the comparatively short duration of the experiment this would form an elegant laboratory exercise for the undergraduate course illustrating the application of the Arrhenius relation in an oscillatory reaction.
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