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Question:

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

Low temperature and high pressure

High temperature and low pressure

Low temperature and low pressure

High temperature and high pressure

Solution:

For the reaction, A2(g) + B2(g) ⇌ X2(g) , ΔrH = −X kJ, a negative ΔrH suggests exothermic nature for the forward reaction. According to Le Chatelier's principle, an exothermic reaction is favored by low temperatures. Furthermore, the reaction involves a decrease in the number of gas molecules (2 moles of reactants to 1 mole of product). Therefore, high pressure will favor the forward reaction, shifting the equilibrium towards the product. Consequently, low temperature and high pressure will favor maximum formation of the product X2(g).