An experiment is described that determines the activation energy (E[subscript a]) of the iodide-catalyzed decomposition reaction of hydrogen peroxide in a much more efficient manner than previously reported in the literature. Hydrogen peroxide, spontaneously or with a catalyst, decomposes to oxygen and water. Because the decomposition reaction is exothermic, the energy released as heat can be treated as a product and used to determine the rate of reaction. Energy transferred as heat is much easier to quantify than changes in molecular concentration because temperature can be measured with a simple thermometer. Measuring the rate of the reaction by monitoring the rate of change in temperature is an alternate and convenient approach to measuring changes in the concentration of hydrogen peroxide or the volume or pressure of oxygen produced throughout the reaction. Because the temperature rises as the reaction progresses, reaction rate data at a range of different temperatures can be collected by students in a single run. The extent of reaction, and thereby the extent of depletion of the peroxide, can be approximated by the reaction temperature relative to the initial and final temperatures. Thus, by using a simple calorimeter and collecting temperature and time data, the activation energy can be determined from an Arrhenius plot. The procedure described for gathering experimental data is easily completed in 30 min or less, so students have the opportunity to repeat their data two or more times within the span of a single lab period. Empirically determining the activation energy of a given reaction is a common and important kinetics experiment in the introductory and advanced chemistry laboratory curriculum, so this methodological innovation may have great appeal to chemical educators.