Chemical equilibrium is a state in a closed system where the rate of a forward chemical reaction is exactly equal to the rate of the reverse chemical reaction. At this point, the net concentrations of the reactants and products remain constant over time, although the chemical reactions themselves are continuously occurring at the molecular level. This state is characterized by a quantifiable relationship between the concentrations of the species involved, which is often expressed by an equilibrium constant. The establishment of equilibrium is dependent on system conditions, such as temperature and pressure; changing these external variables will alter the position of the equilibrium, thereby changing the ratio of product to reactant concentrations.