<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system . Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction . The reaction rates of the forward and backward reactions are generally not zero, but equal . Thus, there are no net changes in the concentrations of the reactant (s) and product (s). Such a state is known as dynamic equilibrium . </P> <P> The concept of chemical equilibrium was developed after Berthollet (1803) found that some chemical reactions are reversible . For any reaction mixture to exist at equilibrium, the rates of the forward and backward (reverse) reactions are equal . In the following chemical equation with arrows pointing both ways to indicate equilibrium, A and B are reactant chemical species, S and T are product species, and α, β, σ, and τ are the stoichiometric coefficients of the respective reactants and products: </P> <Dl> <Dd> α A + β B ⇌ σ S + τ T </Dd> </Dl>

When is equilibrium established in a reversible reaction
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