If we add more of one component, or remove some of another, either the forward or the reverse reaction will be favored; the separate concentrations will adjust, and when equilibrium is restored after the disturbance, the Keq, ratio will be the same as before. Keq varies with temperature, but at a given temperature it is entirely independent of the individual concentrations of reactants and products.

The illustrations on these pages emphasize the fact that the conditions of equilibrium are the same no matter from which side they are approached. Starting from either pure and or pure HI, the reaction eventually will reach equilibrium at the same ratio of products to reactants given by Keq.

In the top picture, the same tank is filled with 2 moles of HI. After a time, measurable quantities of and are present (center). When equilibrium is reached and the composition of the tank becomes constant, the same equilibrium concentrations are observed as before, 0.22 mole each of and , and 1.56 moles of HI.

The equilibrium conditions are the same, no matter what the direction of approach.