Formation of a cloud of vapor above a Pyrex flask demonstrates an exothermic reaction and the action of a catalyst on the rate of reaction. The vapor forms from oxygen gas and steam, products of the exothermic decomposition reaction. Iodide ion from sodium iodide serves as the catalyst. Contains enough material for 7 demos. Includes: hydrogen peroxide, 30%, sodium iodide and instructions. Note: a 1000-mL Pyrex flask is needed but not included.