Chapter summary
Reaction Kinetics, at a glance
Infer a rate law from evidence and explain how concentration, temperature and catalysts change reaction speed.
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 |
|---|---|
| Rate of reaction | The change in concentration of a reactant or product per unit time. |
| Rate equation | An experimentally determined equation, rate = k[A]m[B]n, linking the rate to the concentrations of the reactants. |
| Order of reaction with respect to a reactant | The power to which the concentration of that reactant is raised in the experimentally determined rate equation. |
| Rate constant, k | The proportionality constant in the rate equation. It is constant at a given temperature (and for a given catalyst). |
| Half-life, t1/2 | The time taken for the concentration of a reactant to fall to half of its initial value. |
| Activation energy, Ea | The minimum energy that colliding particles must have for a reaction to occur. |
| Catalyst | A substance that increases the rate of a reaction by providing an alternative pathway with a lower activation energy, and is chemically unchanged at the end of the reaction. |
| Change | Essential explanation |
|---|---|
| Concentration | More particles per volume; collision frequency changes; use the measured order. |
| Temperature | Larger fraction above Ea plus more frequent collisions; k increases. |
| Catalyst | Lower-Ea pathway; distribution unchanged at the same temperature. |
| First-order half-life | Equal times for successive halvings, independent of initial concentration. |
| Enzyme extremes | Active-site shape/interactions change; extremes may denature the protein. |
Quick recall
Define order of reaction with respect to a reactant.