Chapter summary
Chemical Equilibria, at a glance
Explain a changing equilibrium through competing rates, then calculate composition and justify industrial choices.
A-Level 9476 (2026-2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
| Term | Definition to write |
|---|---|
| Dynamic equilibrium | In a closed system, the rate of the forward reaction equals the rate of the backward reaction, and the concentrations of reactants and products remain constant (they are not necessarily equal). |
| Le Chatelier's principle | If a change is made to a system in dynamic equilibrium, the position of equilibrium shifts to reduce the effect of that change. |
| Equilibrium constant, Kc | The ratio of the equilibrium concentrations of the products to those of the reactants, each raised to the power of its coefficient in the balanced equation. It changes only with temperature. |
Dynamic equilibrium means equal forward and reverse rates. A concentration or pressure disturbance can change composition while K stays fixed. Only temperature changes K for the same written reaction; a catalyst speeds approach without changing the endpoint.
Write K from the balanced equation, use equilibrium values and respect phases. Build an amount-change table before converting to concentrations or partial pressures. For Haber, explain yield, rate, compression cost and recycling as distinct considerations.
Quick recall
Define dynamic equilibrium.