QUESTION 5 (Start on a new page.) The reaction of 15 g of an IMPURE sample of calcium carbonate. CaCO3, with EXCESS hydrochloric acid, HCt, of concentration 1,0 mol-dm³, is used to investigate the rate of a reaction. The balanced equation for the reaction is: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(f) + CO2(g) The volume of CO2(g) produced is measured at regular intervals. A sketch graph representing the total volume of carbon dioxide gas produced as a function of time is shown below. Volume CO2(g) (cm³) t₁ t₂ Time (s) 5.1 Define the term reaction rate. (2) 5.2 Give a reason why the gradient of the graph decreases between t₂ and ts. (1) 5,3 Changes in the graph between t, and t₂ are due to temperature changes within the reaction mixture. 5.3.1 Is the reaction EXOTHERMIC or ENDOTHERMIC? (1) 5.3.2 Explain the answer by referring to the graph. (3) 5.4 The percentage purity of the sample is 82,5%.​