Question

Which one of the following conditions will favour maximum formation of the product in the reaction,
A₂(g) + B₂(g) ⇌ X₂(g) Δ_rH = – X kJ ?

• A. Low temperature and high pressure
• B. High temperature and high pressure
• C. Low temperature and low pressure
• D. High temperature and low pressure

Answer 1

The Correct Option is A

To determine which conditions will favor the maximum formation of the product in the given reaction:

\( A_2(g) + B_2(g) \rightleftharpoons X_2(g), \; \Delta_r H = - X \, \text{kJ} \)

we need to consider the effects of temperature and pressure based on Le Chatelier's principle.

1. The reaction is exothermic, as indicated by the negative enthalpy change (\( \Delta_r H = - X \, \text{kJ} \)). According to Le Chatelier's principle, decreasing the temperature will favor the formation of products in an exothermic reaction. Thus, a low temperature is desirable.
2. For the pressure conditions, we should look at the change in the number of moles of gas. In this case, \( 1 \, \text{mol} \) of \( A_2 \) and \( 1 \, \text{mol} \) of \( B_2 \) (total \( 2 \, \text{mol} \)) react to form \( 1 \, \text{mol} \) of \( X_2 \). This reduces the total moles of gas.
3. According to Le Chatelier's principle, increasing the pressure favors the side with fewer moles of gas. Since the product side has fewer moles, increasing the pressure will shift the equilibrium towards the product formation.

Therefore, the conditions that favor maximum formation of the product are:

• Low Temperature: To favor the exothermic reaction.
• High Pressure: To favor the side with fewer gas moles.

Hence, the correct option is Low temperature and high pressure.