Dynamic equilibrium in a closed system

A reversible reaction can proceed in both directions: reactants form products in the forward reaction, while products form reactants in the reverse reaction.

In a closed system, no reactants or products can escape. As the reaction proceeds, their amounts change. The system may eventually reach a state in which the amounts of reactants and products remain constant. This state is called dynamic equilibrium.

At dynamic equilibrium, both reactions are still happening, but the forward and reverse reactions occur at exactly the same rate. Each substance is formed as quickly as it is used up, so there is no overall change in its amount.

The equilibrium is dynamic because the reactions have not stopped. Constant amounts do not mean that the amounts of reactants and products are equal; they mean that the opposing reaction rates are equal.