The reaction between calcium carbonate and dilute hydrochloric acid produces carbon dioxide and it is therefore easy to follow the progress of the reaction by measuring the volume of gas evolved with time. You will use the graph of volume against time to measure the initial gradient of the graph, which is the rate of the reaction in cm 3 /s. The data is then used to construct a new graph showing the variation of the rate with the concentration of the acid used. The graph can then be used to predict the rate of the reaction at another concentration. This prediction can then be tested by running a new simulation.