A product is a substance that forms as a result of a biological- or chemical reaction. While the end product of some chemical reactions may be the result of a relatively rapid reaction, nanoseconds to seconds, chemical equilibria in complex systems may require years or even centuries to be established. For example, equilibria in groundwater systems with multiple components are achieved on timescales of millennia, if ever. When a chemical change occurs, reactants are rearranged. The result of these rearrangements is the formation of new, different substances (products)