Question

The Le Chatelier’s principle is applicable to physical and chemical equilibria. 

1. What are the factors which can influence the equilibrium state of a system? 

2. Explain the factors affecting the chemical equilibrium on the basis of Le Chatelier’s principle taking Haber’s process for the manufacture of ammonia as an example.

Answer 1

1. The following factors can influence the equilibrium state of a system: 

• Change in concentration of the reactants or products.
• Change in temperature.
• Change in pressure.
• Addition of inert gas.
• Presence of catalyst.

2. N₂(g) + 3H₂(g) ⇌ 2NH₃ (g); ∆_rH = -91.8 kJ mol^-1

When concentration of N or H is increased, a good yield of NH can be achieved. The rate of forward reaction can also be increased by removing NH from the reaction mixture.

When pressure is increased, the system will try to decrease pressure and for this system will proceed in that direction where there is minimum number of moles i.e., forward reaction. Thus, a good yield of NH₃ can be achieved by increasing pressure.

Since the formation of NH₃ is an exothermic reaction, a good yield of NH₃ can be achieved by decreasing the temperature. But if the temperature is decreased to very low value the reactant molecules do not have sufficient energy to interact. Hence, an optimum temperature of 500°C is used.