IP Chemistry Upper Sec 09: Chemical Energetics
Enthalpy change, exothermic/endothermic profiles, and bond energy ideas for IP Sec 3-4 Chemistry (O-Level 6092, 2026).
These notes align with SEAB GCE O-Level Chemistry (6092) content used in IP programmes (exams from 2026).
Status: SEAB O-Level Chemistry 6092 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.
The core idea is simple: Energetics asks whether heat is released or absorbed.
Use it as a working check: Exothermic reactions have products lower in energy and negative enthalpy change. Endothermic reactions have products higher in energy and positive enthalpy change.
Then go one layer deeper: Example: bond breaking absorbs energy and bond making releases energy. A reaction is exothermic when making new bonds releases more energy than breaking old bonds absorbs.
What you must know
- Enthalpy change is heat change at constant pressure; exothermic releases heat (ΔH < 0), endothermic absorbs heat (ΔH > 0).
- Energy profile diagrams must show relative energy of reactants/products, activation energy peak, and ΔH arrow.
- Bond breaking is endothermic; bond making is exothermic; overall ΔH is “energy to break − energy released making.”
- Qualitative bond-energy comparisons explain why combustion is strongly exothermic and why thermal decompositions need heating.
Use this checkpoint before drawing or explaining an energy profile.
| Profile decision | Exothermic reaction | Endothermic reaction |
| Product energy level | Products lower than reactants | Products higher than reactants |
| Enthalpy-change sign | Negative, because heat is released | Positive, because heat is absorbed |
| Enthalpy-change arrow | Down from reactants to products | Up from reactants to products |
