A rate law model for the explanation of complex pH oscillations in the thiourea–iodate–sulfite flow system

Abstract

In a continuous flow stirred tank reactor (CSTR), the reaction of thiourea–iodate–sulfite (TuIS) exhibits a rich variety of complex oscillations in pH. The transitions from 1ⁿ type oscillations to 1³, 1² type and simple oscillations were observed on decreasing the flow rate gradually in small steps at 30.2 °C and 20.5 °C, respectively. The transitions from 1ⁿ type oscillations to 1⁰1⁴, 1⁰1³ type and simple oscillations were observed as well on increasing the temperature in small steps at a given flow rate. Based on the analogous iodate–sulfite–thiosulfate system a simple empirical rate law model is suggested to give a sound agreement between the experimental and simulated results on the complex oscillatory behaviour. A possible explanation of the emergence of the simple empirical rate law model from the mechanism of the individual reactions of the TuIS system is also discussed.