Temperature and Reversible Reactions

Le Chatelier’s Principle Recap

If a system at equilibrium is disturbed by changing conditions, the system responds to counteract the change.

Example Reaction

2NO_2(g)\rightleftharpoons N_2O_4\left(g\right)

  • Forward reaction = exothermic (releases energy, increases temperature).

  • Reverse reaction = endothermic (takes in energy, decreases temperature).

Effect of Temperature Changes

  1. Increase temperature

    • Equilibrium shifts to endothermic direction (absorbs energy).

    • Here → shifts left (reverse reaction).

    • More NO₂ formed, less N₂O₄.

  2. Decrease temperature

    • Equilibrium shifts to exothermic direction (releases energy).

    • Here → shifts right (forward reaction).

    • More N₂O₄ formed, less NO₂.

✅ Key Idea:

  • Raising temperature favours the endothermic reaction.

  • Lowering temperature favours the exothermic reaction.

  • Exam questions will always tell you which direction is exothermic/endothermic.