GCSE Chemistry · AQA 8462 · Topic 4.6.2
Reversible reactions and dynamic equilibrium
Key points
- In a reversible reaction products can react to form the reactants again, shown by , e.g. ammonium chloride ammonia + hydrogen chloride.
- The energy transferred is the same in both directions: if the forward reaction is exothermic, the reverse is endothermic. Hydrated copper sulfate (blue) ⇌ anhydrous copper sulfate (white) + water is a good example.
- In a closed system, a reversible reaction reaches equilibrium when the forward and reverse reactions occur at exactly the same rate; concentrations then stay constant.
- (Higher) Le Chatelier's principle: if conditions change, the position of equilibrium shifts to counteract the change.
- (Higher) Raising temperature shifts equilibrium in the endothermic direction; lowering it favours the exothermic direction.
- (Higher) Increasing pressure shifts equilibrium to the side with fewer molecules of gas; increasing the concentration of a reactant makes more product.
Topic notesPremium
Some reactions can go in both directions. When a reversible reaction takes place in a sealed container, it reaches a balance called dynamic equilibrium, and (Higher tier) changing the conditions moves that balance.
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