Question

For the reversible reaction :
\(N_2(g) + 3H_2(g) ⇋ 2NH_3(g) + \text {Heat}\)
The equilibrium shifts in forward direction :

• A. By decreasing the pressure
• B. By decreasing the concentrations of N₂(g) and H₂(g)
• C. By increasing pressure and decreasing temperature
• D. By Increasing the concentration of NH₃(g)

Answer 1

The Correct Option is C

The given reaction is:

\(N_2(g) + 3H_2(g) ⇋ 2NH_3(g) + \text {Heat}\)

This is an exothermic reaction meaning that heat is released when forming ammonia. Let's analyze the factors affecting this equilibrium:

Key Concepts:

• Based on Le Chatelier's Principle, the position of equilibrium will shift in a direction that opposes the change made to the system.
• For an exothermic reaction, increasing the temperature favors the reverse reaction (endo direction), whereas decreasing the temperature favors the forward reaction (exo direction).
• For gaseous reactions involving different moles of gas, a change in pressure can shift the equilibrium. An increase in pressure favors the side with fewer gaseous moles.

Analysis of Options:

1. By decreasing the pressure: The forward reaction results in a decrease in total number of moles of gas (from 4 moles of reactants to 2 moles of ammonia). Therefore, decreasing pressure would shift the equilibrium towards the side with more gas moles, i.e., reactants. This is incorrect.
2. By decreasing the concentrations of \(N_2\)(g) and \(H_2\)(g): Reducing the concentration of reactants will shift the equilibrium towards the reactants to compensate for the change. This is incorrect.
3. By increasing pressure and decreasing temperature: Increasing pressure shifts the equilibrium towards fewer moles of gas, favoring the formation of ammonia. Decreasing temperature makes the system favor the exothermic forward reaction. Thus, this shifts the equilibrium in the forward direction. This is the correct option.
4. By increasing the concentration of \(NH_3\)(g): Increasing product concentration will shift the equilibrium towards the reactants (reverse direction) to reduce the product concentration. This is incorrect.

Conclusion:

The equilibrium shifts in the forward direction (formation of ammonia) when the pressure is increased and the temperature is decreased, which corresponds to option 3.