After the forward and reverse reactions proceed for a suitable length of time, the concentrations of A and B will settle down to a fixed ratio, which will not depend on the starting conditions or the absolute number of A and B molecules present. This is the condition of equilibrium, at which forward and reverse rates are exactly in balance:





Equilibrium does not imply that all chemical activity has stopped, only that forward and reverse reactions are proceeding at the same rate, so no further net change in the amounts of reactants and products occurs.