The theory of chemical equilibrium explains how chemical reactions reach a state where the rates of the forward and reverse reactions are equal. In this state, the concentrations of reactants and products remain constant over time, even though both reactions continue to occur. This balance can be affected by changes in conditions such as temperature, pressure, and concentration, which can shift the equilibrium position. In a chemical equation, the equilibrium constant, represented as K, quantifies the ratio of product concentrations to reactant concentrations at equilibrium. Understanding this theory is essential in fields like chemistry, biochemistry, and industrial processes, where controlling reactions is crucial for desired outcomes.