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.