A student adds an excess of magnesium ribbon to 50.0 cm3 of dilute hydrochloric acid and measures the volume of hydrogen produced. Mg + 2HCl → MgCl2 + H2 The experiment is carried out again with acid of concentration 0.400 mol/dm3 in place of 0.200 mol/dm3. Everything else is kept the same, and the reaction is found to be faster.