A simple method for studying the kinetics of a chemical reaction is described and the significance of reaction orders in deducing reaction mechanisms is demonstrated. In this student laboratory experiment, oxidation of iodide by iron(III) ions in an acidic medium is transformed into a clock reaction. By means of the initial rates method, it is found that the reaction is second order with respect to iodide and first order with respect to iron(III) ions. Having established the rate law, the students are encouraged to propose a possible mechanism for the reaction investigated. (Contains 4 figures.)