mass action rate law for third order forward, reversible reactions, one reactant mass action rate law for third order forward, third order reverse, reversible reactions, one reactant Reaction scheme where the products are created from the reactants and the change of a product quantity is proportional to the product of reactant activities. The reaction scheme does include a reverse process that creates the reactants from the products. The rate of the forward process is proportional to the cube of one reactant quantity. The rate of the reverse process is proportional to the quantity of three products.