Question

For the reaction in equilibrium:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ΔH = -Q
Reaction is favoured in forward direction by:

• A. use of catalyst
• B. decreasing concentration of N₂
• C. low pressure, high temperature and high concentration of ammonia
• D. high pressure, low temperature and higher concentration of H₂

Answer 1

The Correct Option is D

To determine the correct conditions under which the forward reaction is favored for the equilibrium: 

\(\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -Q\)

Let's analyze the factors influencing this reaction:

1. Le Chatelier's Principle: This principle helps determine how a change in conditions affects chemical equilibria. According to this principle, the equilibrium will shift to counteract the change applied.
2. Effect of Pressure: The reaction involves 4 moles of reactants (1 mole of \(\text{N}_2\)and 3 moles of \(\text{H}_2\)) forming 2 moles of products (2 moles of \(\text{NH}_3\)). An increase in pressure will shift the equilibrium towards the side with fewer moles of gas, which is the forward direction, forming ammonia.
3. Effect of Temperature: The reaction is exothermic (as indicated by \(\Delta H = -Q\)), meaning heat is released. Lowering the temperature favors the exothermic reaction, hence steering the equilibrium to the right.
4. Effect of Concentration: Increasing the concentration of hydrogen \((\text{H}_2)\)will shift the equilibrium to favor the forward reaction, as it will try to reduce the concentration by producing more ammonia.
5. Use of Catalyst: A catalyst speeds up the rate of both the forward and reverse reactions equally, but it does not change the equilibrium position. Thus, it does not favor the forward reaction in terms of equilibrium position.

Considering these points, the correct answer is high pressure, low temperature, and higher concentration of \(\text{H}_2\), which would drive the equilibrium position towards the production of more ammonia, as justified by Le Chatelier's principle.

Conclusion: The option high pressure, low temperature, and higher concentration of H2 correctly describes the conditions that favor the forward direction of this equilibrium reaction.