Le Chatelier's Principle for Gas-Phase Equilibrium

Steps:

• Reaction Q(g) ⇌ 2R(g) has 1 mol gas on left, 2 mol on right; forward is endothermic (ΔH > 0).
• Shifting right favors products (2R).
• Increasing flask volume decreases pressure.
• Equilibrium shifts right to produce more moles of gas, opposing the pressure change.

Why D is correct:

• Increasing volume lowers pressure; Le Chatelier's principle shifts equilibrium toward side with more gas moles (right, 2 vs. 1).

Why the others are wrong:

• A: Catalyst speeds both directions equally, no shift in position.
• B: Decreasing temperature favors exothermic reverse reaction, shifting left.
• C: Increasing pressure favors side with fewer gas moles (left, 1 vs. 2), shifting left.

Final answer: D