Chapter summary
Chemical Energetics, at a glance
Track energy through bonds and cycles, then combine enthalpy and entropy to assess thermodynamic feasibility.
A-Level 9476 (2026-2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
Heat gained by the solution is heat lost by the reaction. Hess cycles require identical endpoint states. Bond-energy estimates use gaseous bonds broken minus gaseous bonds formed. The syllabus lattice energy is negative for lattice formation; dissolution uses its reverse plus hydration.
ΔG° = ΔH° - TΔS° with T in K and matching units. Heating favours processes with positive ΔS. A negative standard free-energy change indicates a thermodynamic tendency under standard conditions, not a guaranteed fast or complete reaction.