Chapter summary
Chemical Energetics, at a glance
Explain temperature changes and the energy cost of rearranging particles.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
| Term | Definition to write |
|---|---|
| Exothermic reaction | A reaction that transfers energy, usually as heat, to the surroundings, so the temperature of the surroundings rises. |
| Endothermic reaction | A reaction that takes in energy, usually as heat, from the surroundings, so the temperature of the surroundings falls. |
Pure only
| Term | Definition to write |
|---|---|
| Enthalpy change, ΔH | The heat energy change of a reaction. ΔH is negative for an exothermic reaction and positive for an endothermic reaction. |
| Activation energy, Ea | The minimum energy that colliding particles must have for a reaction to occur. |
Exothermic: energy out to surroundings. Endothermic: energy in from surroundings. Use the initial change and account for later heat exchange.
Pure only
Pure: ΔH compares product and reactant levels; Ea is the barrier. Breaking bonds absorbs energy; making bonds releases it. Compare both totals.
Quick recall
What is an exothermic reaction?