A forward reaction is a reversible reaction in which reactants produce products, and a reverse reaction turns those products into their original reactants. There are also nonreversible reactions, in which products are formed, reactants are completely consumed and the process ends.
During reversible reactions, both the reverse reaction and forward reaction rates occur at the same rate, which means that the mixture has reached chemical equilibrium. This occurs when a chemical reaction is put inside a closed vessel, unlike stiochemistry calculations in which reactions run to completion. Examples of nonreversible reactions are metabolizing glucose and burning a piece of paper.