# Features Of Equilibrium Constant

(1) The value of equilibrium constant is independent of the original concentration of reactants.

(2) The equilibrium constant has a definite value for every reaction at a particular temperature. However, it varies with change in temperature.

(3) For a reversible reaction, the equilibrium constant for the forward reaction is inverse of the equilibrium constant for the backward reaction.

In general, K_{forward reation} = (1/K'_{backward})

(4) The value of equilibrium constant tells the extent to which a reaction proceeds in the forward or reverse direction.

(5) The equilibrium constant is independent of the presence of catalyst.

(6) The value of equilibrium constant changes with the change of temperature. Thermodynamically, it can be shown that if K_{1} and K_{2} be the equilibrium constants of a reaction at absolute temperatures T_{1} and T_{2}. If ΔH is the heat of reaction at constant volume,

Then

_{} ^{(Van’t Hoff equation)}

The effect of temperature can be studied in the following three cases

(i) When ΔH = 0 i.e., neither heat is evolved nor absorbed

log K_{2} – log K_{1} = 0 or log K_{2} = logK_{1} or K_{2} = K_{1 }

Thus, equilibrium constant remains the same at all temperatures.

(ii) When ΔH = +ve i.e., heat is absorbed, the reaction is endothermic. The temperature T_{2} is higher than T_{1}.

log K_{2} – log K_{1} = +ve or log K_{2} = logK_{1} or K_{2} = K_{1 }

The value of equilibrium constant is higher at higher temperature in case of endothermic reactions.

(iii) When ΔH = – ve, i.e., heat is evolved, the reaction is exothermic. The temperature T_{2} is higher than T_{1}.

log K_{2} – log K_{1} = +ve or log K_{1} = log K_{2} or K_{2} = K_{1 }

The value of equilibrium constant is lower at higher temperature in the case of exothermic reactions.

(7) The value of the equilibrium constant depends upon the stoichiometry of the chemical equation.

For the reaction

(i) Similarly, if a particular equation is multiplied by 2, the equilibrium constant for the new reaction (K¢) will be the square of the equilibrium constant (K) for the original reaction i.e., K = K^{2}

(ii) If the chemical equation for a particular reaction is written in two steps having equilibrium constants K_{1} and K_{2}, then the equilibrium constants are related as

K = K_{1} × K_{2}