Chapter summary
Chemical Equilibria, at a glance
Explain a changing equilibrium, calculate its composition and connect the Haber process to rate and yield.
A-Level 8873, revised syllabus (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. |
| Question | Reasoning |
|---|---|
| Which way does equilibrium shift? | Use the imposed concentration, gas-volume or temperature change and the balanced equation. |
| Does Kc change? | Only a temperature change changes Kc for the same written reaction. |
| How fast is equilibrium reached? | Use kinetics; a catalyst changes the approach, not the equilibrium composition. |
Kc: equilibrium concentrations, products over reactants, coefficient powers. Convert amounts using the final volume. Link changes by stoichiometry and reject negative concentrations.
Haber: high pressure favours fewer gas moles; lower temperature favours the exothermic equilibrium but slows reaction. Iron gives a faster approach; cooling separates ammonia and reactants are recycled.
Quick recall
Define dynamic equilibrium.