Q.

1. If NH3 is added to the equilibrium system of Haber process, in which direction will the equilibrium shift to consume added NH3 so as to reduce the effect of stress?
2. In this process, out of the reverse and forward reaction, which reaction will occur to a greater extent due to this stress ?
3. What will be the effect of this stress on the yield of NH3 ?

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 …