A-Level Physical Chemistry: Energetics, Enthalpy and Thermodynamics

Across the main A-level chemistry boards, this part of physical chemistry usually begins with energy changes in reactions and then develops into entropy and Gibbs free energy at full A level. The terminology varies slightly by board, but the core syllabus is very similar.

1. What you study first: energetics / enthalpy

This is usually the foundation section and is commonly taught in the earlier AS or shared part of the course.

Exothermic and endothermic reactions
Enthalpy change, ΔH
Standard enthalpy changes, especially formation and combustion
Often enthalpy of neutralisation
Reaction profile / enthalpy level diagrams
Calorimetry using q = mcΔT
Hess's law and enthalpy cycles
Mean bond enthalpies / bond energies for estimating ΔH

2. What gets added later: thermodynamics

At full A level, the topic becomes more advanced and focuses on why reactions are feasible and how energy and disorder interact.

Lattice enthalpy / lattice energy
Born–Haber cycles
Enthalpy of hydration
Enthalpy of solution
Entropy, ΔS, as a measure of disorder or energy dispersal
Predicting entropy changes
Gibbs free energy, ΔG = ΔH − TΔS
Using ΔG to judge feasibility
Understanding how temperature affects feasibility

3. Typical calculations and skills

Calculating heat energy from q = mcΔT
Converting experimental heat data into molar enthalpy changes
Using Hess cycles
Estimating enthalpy changes from bond enthalpies
Calculating values in Born–Haber cycles
Calculating or interpreting entropy changes
Using ΔG = ΔH − TΔS
Finding the temperature at which a reaction becomes feasible

        This is one of the more calculation-heavy sections of A-level physical chemistry, so students are expected to understand both the concepts and the mathematical relationships.
      

4. Practical work linked to the topic

Measuring temperature changes in calorimetry
Determining enthalpy changes experimentally
Considering heat loss and experimental error
Using practical results in enthalpy calculations

5. By exam board

AQA

Energetics is part of core physical chemistry. Thermodynamics is explicitly A-level only and includes Born–Haber cycles, entropy and Gibbs free energy.

OCR A

Students meet enthalpy changes in Module 3, then study enthalpy, entropy and free energy later in Module 5.

Edexcel

The content is split into Energetics I and Energetics II, with the later section covering lattice energy and entropy / Gibbs free energy.

Cambridge International

AS includes enthalpy change and Hess's law. Full A level adds lattice energy, hydration / solution enthalpy, entropy and ΔG.

6. One-sentence summary

In short, this part of the syllabus is about how energy changes in chemical reactions are measured and calculated, and how enthalpy and entropy together determine whether reactions are feasible.