gen-define-le-chatelier-s-principle-and-give-one-short-worked-ex-00f5

Define Le Chatelier's principle and give one short worked example.

# Le Chatelier's Principle **Definition:** When a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will shift its equilibrium position in a direction that counteracts the imposed change. In simpler terms: *A system at equilibrium responds to stress by shifting to relieve that stress.* ## Worked Example **Consider the equilibrium:** $$\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -92 \text{ kJ/mol}$$ **Question:** What happens if we increase the temperature? **Solution:** - The reaction is exothermic (releases heat, negative ΔH) - We can think of heat as a "product": N₂ + 3H₂ ⇌ 2NH₃ + heat - Increasing temperature = adding heat to the system - By Le Chatelier's principle, the system shifts to counteract this change - **The equilibrium shifts LEFT** (toward reactants) to consume the added heat - **Result:** Less NH₃ is produced at higher temperatures This is why the Haber process for ammonia production uses moderate temperatures (400-450°C) rather than high temperatures—even though higher temperatures increase reaction rate, they decrease the equilibrium yield.