For a given reaction A_2(g) + 3B2_2(g) ⇋ 2AB_3(g), ΔH = —ve

For this reaction, the favorable condition for decomposition of AB₃ is: 

CONCEPT:

Le Chatelier's Principle

• Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.
• For a reaction involving gases, the effect of pressure and temperature can be analyzed as follows:
  • Pressure: Increasing pressure favors the side with fewer moles of gas, while decreasing pressure favors the side with more moles of gas.
  • Temperature: For an exothermic reaction (ΔH = —ve), increasing temperature shifts the equilibrium toward the reactants (decomposition), while decreasing temperature favors the products.

EXPLANATION:

• The given reaction is:

  A₂(g) + 3B₂(g) ⇋ 2AB₃(g), ΔH = —ve

• To favor the decomposition of AB₃ (i.e., shifting the equilibrium toward the reactants A₂ and B₂), we analyze the conditions:
  • Effect of Pressure: The forward reaction forms 2 moles of AB₃ from 4 moles of reactants (1 mole of A₂ and 3 moles of B₂). Decreasing pressure will favor the backward reaction since it produces more moles of gas.
  • Effect of Temperature: The reaction is exothermic (ΔH = —ve). Increasing temperature will favor the backward (endothermic) reaction, leading to decomposition of AB₃.

Therefore, the favorable condition for decomposition of AB₃ is high temperature and low pressure.