To measure the rate of a chemical reaction, we measure how quickly the products are formed or how quickly the reactants are used up. We record the change in the amount of reactant or product - change in mass or volume - and the time that change takes, measured at evenly spaced intervals. Some reactions like rusting are slow, and some are fast like zinc and sulfuric acid. Change in mass is used to measure escaping gas, Animated diagrams also show us how to measure the volume of escaping gas.