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, Kforward 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 K1 and K2 be the equilibrium constants of a reaction at absolute temperatures T1 and T2. If ΔH is the heat of reaction at constant volume,
(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 K2 – log K1 = 0 or log K2 = logK1 or K2 = K1
Thus, equilibrium constant remains the same at all temperatures.
(ii) When ΔH = +ve i.e., heat is absorbed, the reaction is endothermic. The temperature T2 is higher than T1.
log K2 – log K1 = +ve or log K2 = logK1 or K2 = K1
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 T2 is higher than T1.
log K2 – log K1 = +ve or log K1 = log K2 or K2 = K1
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 = K2
(ii) If the chemical equation for a particular reaction is written in two steps having equilibrium constants K1 and K2, then the equilibrium constants are related as
K = K1 × K2