Q.How does the change of pressure affect the value of equilibrium constant ?

Applying Le Chatelier's principle to each factor in turn: (1) Concentration -- increasing the concentration of a reactant or product shifts equilibrium in the direction that consumes the added species (e.g. adding extra H2 to the Haber equilibrium $N_2(g)+3H_2(g)\rightleftharpoons 2NH_3(g)+\text{Heat}$ shifts it forward, increasing NH3 yield); the value of $K_c$ itself is unaffected. (2) Pressure/volume -- only affects equilibria where the number of gas moles differs between reactants and products; decreasing pressure (increasing volume) shifts equilibrium toward the side with MORE gas moles (e.g. $N_2O_4(g)\rightleftharpoons 2NO_2(g)$ shifts right, deepening its brown colour, when pressure is decreased), while increasing pressure shifts it toward the side with FEWER gas moles; again $K_c$ is unaffected. (3) Temperature -- increasing temperature shifts equilibrium in the endothermic direction (e.g. for the exothermic forward reaction $CO(g)+2H_2(g)\rightleftharpoons CH_3OH(g)+\text{Heat}$, raising temperature shifts equilibrium left, and unlike concentration/pressure changes, this genuinely changes the numerical VALUE of $K_c$, which falls as temperature rises for an exothermic forward reaction). (4) Catalyst -- speeds up both the forward and reverse reactions equally (by lo …