Answer. The amounts of reactants and products do not change in reversible reactions because these reactions establish equilibrium state. At equilibrium state rates of consumption and reformation of reactants are equal. Similarly, rates of formation and decomposition of products are equal. So, the amount of reactants consumed is reproduced at the same moment. Similarly, the amount of products produced is simultaneously used to reform the reactants. Therefore, amounts of reactants and products do not change in reversible reaction.