Thermokinetics: Iodide-Catalyzed Decomposition Kinetics of Hydrogen Perioxide. An Initial-Rate Approach

Abstract

A temperature-based determination of the kinetics of the H2O2 decomposition using the method of initial rates is described. The reagents (total volume 5 mL) are added to a microcalorimeter and the temperature–time data are collected using a temperature sensor and a datalogger. The temperature–time plots are linear for a considerable length of time allowing for a straightforward and accurate determination of the initial rate, dT/dt. Changing from dT/dt to an initial rate in terms of H2O2 concentration (–d[H2O2]/2dt), requires the determination of the enthalpy of the reaction as well as the heat capacity of the microcalorimeter. In doing so, this lab combines thermochemistry and kinetics. The reaction is first order with respect to the catalyst, [I–], and first order with respect to [H2O2]. The average rate constant reported by students is 0.0108 ± 0.0003 L mol–1 s–1 at ~20 °C.