2025 H2 Chem P1 Q27 — Thermodynamics Solution

The answer is A (\(-625\ \text{kJ mol}^{-1}\)).
Number of electrons transferred: \(2\text{Cr} \rightarrow 2\text{Cr}^{3+} + 6\text{e}^-\) and \(3\text{Cu}^{2+} + 6\text{e}^- \rightarrow 3\text{Cu}\), so \(n = 6\).
\(\Delta G^{\ominus} = -nFE^{\ominus}_\text{cell} = -6 \times 96500 \times 1.08 = -625\,320\ \text{J mol}^{-1} = -625\ \text{kJ mol}^{-1}\)
• B is wrong: \(-313\ \text{kJ mol}^{-1}\) uses \(n = 3\).
• C is wrong: \(-208\ \text{kJ mol}^{-1}\) uses \(n = 2\).
• D is wrong: \(-104\ \text{kJ mol}^{-1}\) uses \(n = 1\).