Calcium metal + water → calcium hydroxide + hydrogen gas calcium and water are the reactants in this chemical reaction, whereas calcium hydroxide and hydrogen gas are the products that are formed. once the reaction reaches completion, a. the total mass of the products will be greater than the original mass of the reactants. b. the products of the reaction will have changed back into the reactants. c. the total mass of the products will be equal to the original mass of the reactants. d. the total mass of the products will be less than the original mass of the reactants.