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Equilibrium (⇌) is achieved when the concentration of the forward rate of reaction and the reverse rate of reaction are equal.

It does not mean that the reaction stops when the equilibrium is achieved. In contrast, the reaction is continued and the rate of the products being formed is equal to the rate of the reactants being converted back.

For example, for the reaction, A + B ⇌ C + D, at equilibrium:

Kc = [C][D] / [A][B]

Kc - the equilibrium constant, a characteristic of a given reaction.

For the reaction: vaA + vbB ⇌ vcC + vdD, where va, vb, vc and vd represent the stoichiometry factors of the form ‘products/reactants’:

Kc = [C]vc[D]vd / [A]va[B]vb[1].


  1. Murphy, B. and Hathaway, C. A working method approach for introductory physical chemistry calculations numerical and graphical problem solving. Cambridge : Royal Society of Chemistry. 1997
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