Le Chatelier's Principle for Endothermic Gas Equilibrium

Steps:

• Count gaseous moles: 2 HI(g) on left, 1 I₂(g) + 1 H₂(g) on right—equal, so pressure change does not shift equilibrium.
• Note ΔH = +12 kJ mol⁻¹: forward reaction endothermic, increasing temperature favors products to absorb heat, shifting right.
• Apply Le Chatelier's principle: system opposes changes; equal moles mean no pressure response, but heat addition drives endothermic direction.

Why D is correct:

• Aligns with Le Chatelier's principle: unchanged mole count ignores pressure; endothermic forward shifts right with higher temperature.

Why the others are wrong:

• A: Pressure cannot shift right—moles equal, no volume change incentive.
• B: Pressure cannot shift left—moles equal, no effect.
• C: Temperature shift is wrong—endothermic reaction moves right, not left, with heat increase.

Final answer: D