Solid calcium carbonate is added to 100 cm³ of dilute hydrochloric acid and the rate of the reaction is measured. 100 cm³ of distilled water is then added to a second 100 cm³ portion of the acid, and the experiment repeated under the same conditions. Why does the addition of water decrease the rate of the reaction? 1 Adding water reduces the frequency of collisions between reactant molecules. 2 Adding water reduces the proportion of effective collisions between reactant molecules. 3 Adding water reduces the proportion of reactant molecules possessing the activation energy.