The rate of a chemical reaction can be found by measuring the quantity of a reactant used or the quantity of product formed over time: mean rate o f reaction = quantity o f reactant used time taken mean rate o f reaction = quantity o f product formed time taken The quantity of reactant or product can be measured by the mass in grams or by a volume in cm3. The units of rate of reaction may be given as g/s or cm3/s. For the Higher Tier, students are also required to use quantity of reactants in terms of moles and units for rate of reaction in mol/s. Students should be able to: • calculate the mean rate of a reaction from given information about the quantity of a reactant used or the quantity of a product formed and the time taken • draw, and interpret, graphs showing the quantity of product formed or quantity of reactant used up against time • draw tangents to the curves on these graphs and use the slope of the tangent as a measure of the rate of reaction