A-Level Chemistry: Equilibria & Le Chatelier: Worked Examples

Dynamic equilibrium

Forward and backward reactions occur at equal rate, concentrations stay constant. Position can shift with conditions.

Le Chatelier’s principle

If a system is disturbed, it shifts to oppose the change. Add reactant → shift to products. Increase pressure → shift to side with fewer gas molecules.

Exam habits

• Always state both direction of shift AND effect on yield.
• Don’t forget temperature: exothermic favours lower T, endothermic favours higher T.
• Use Kc/Kp to reason quantitatively if asked.