A-Level Chemistry: Thermodynamics
Thermodynamics is the most mathematically demanding physical chemistry topic at A-level, and its questions punish both sloppy definitions and sloppy units. This quiz covers the Year 2 apparatus in full, with the arithmetic of every numeric answer independently recomputed during verification.
The Born-Haber questions work at both levels the exam does. Definitionally, the first electron affinity is pinned down precisely — gaseous atoms gaining electrons to form gaseous ions, the step students most often mislabel in a cycle. Computationally, a full magnesium chloride cycle must be assembled and solved for the lattice enthalpy, handling the doubled chlorine atomisation and electron affinity terms that make MgCl₂ the classic stumbling block.
Lattice enthalpy reasoning is tested through its two determinants — ionic charge and ionic radius — and applied comparatively: why magnesium oxide, with its 2+/2− ions, out-bonds every 1+/1− competitor. The solution chemistry questions connect lattice dissociation and hydration enthalpies into the enthalpy of solution, with the always-exothermic character of hydration explained through ion-dipole attraction.
Entropy is covered from prediction (melting and dissolving raise it; a gas-consuming reaction like hydrogen combustion lowers it) through to the Gibbs equation, where the feasibility-temperature calculation — T = ΔH/ΔS with the kilojoule-to-joule conversion done correctly — lands at 333 K. That unit conversion is precisely where this question type is usually lost.
The blind-solver verification pass returned complete agreement across all ten questions. Together with the Energetics quiz in this collection, this set completes the enthalpy story from Year 1 cycles to Year 2 feasibility.
- Identify and define every step in a Born-Haber cycle
- Solve a full Born-Haber cycle for lattice enthalpy, handling doubled anion terms
- Explain lattice enthalpy magnitudes through ionic charge and radius
- Connect lattice, hydration and solution enthalpies
- Predict entropy signs and calculate feasibility temperatures with ΔG = ΔH − TΔS
Aligned to the thermodynamics content of the DfE A level science subject content as delivered in current specifications: Born-Haber cycles, lattice enthalpy, enthalpies of solution and hydration, entropy and Gibbs free energy.
Sample question
In a Born-Haber cycle for NaCl, which specific enthalpy change represents the energy required to convert one mole of gaseous chlorine atoms into one mole of gaseous chloride ions?
- Enthalpy of atomisation of chlorine
- First ionisation energy of chlorine
- First electron affinity of chlorine
- Lattice enthalpy of NaCl
See the answer
First electron affinity of chlorine
The first electron affinity is defined as the enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous 1- ions.