Chapter summary
Chemical Energetics: Thermochemistry, at a glance
Read reaction energy, measure heat and use supplied cycles without losing signs or stoichiometric factors.
A-Level 8873, revised syllabus (2026-2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
| Step | Remember |
|---|---|
| Sign | Exothermic reaction negative; its surroundings gain heat. |
| One mole of what? | Formation: compound; combustion: fuel; neutralisation: water; lattice: solid. |
| Calorimetry | q = mcDeltaT; use all heated solution mass; reaction heat is -q. |
| Hess cycle | Reverse arrow → reverse sign; scaled equation → scaled enthalpy. |
| Bond energies | Broken minus formed, using gas-phase bonds. |
| Lattice comparison | Higher charges/smaller ions → greater magnitude, more negative formation energy. |