On the basis of Le Chatelier principle explain how temperature and pressure can be adjusted to increase the yield of ammonia in the following reaction.

N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g) Δ H = -92.38 kJ mil^-1

What will be the effect of addition of argon to the above reaction mixture at constant volume?

Given, N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g), Δ H = -92.38 kJ mol^-1

• Since ΔH is negative that means forward reaction is exothermic.

• Now according to Le Chatelier principle, if the temperature is decreased the reaction will move in forward direction and more yield of product will be obtained.

• But if the temperature is increased the reaction will move in backward direction and yield of product will be less.

• According to Le Chatelier principle, if the pressure is increased the Equilibrium will shift in a direction where the numbers of gas molecules are less. Therefore, on increasing the pressure the Equilibrium will shift in forward direction and yield of product will be increased.

Number of moles of reactants = 1 + 3 = 4

Number of moles of product = 2

• Therefore, low temperature and high pressure are favourable conditions to increase the yield of products.

• Adding an inert gas at constant volume does not result in a shift. This is because the addition of a non-reactive gas does not change the partial pressures of the other gases in the container.