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The Gibbs free energy change (ΔG) is a key factor in metallurgical processes. At 800°C, the ΔG values for the following reactions are provided: S2(s) + 2O2(g) → 2SO2(g); ΔG = −544 kJ 2Zn(s) + S2(s) → 2ZnS(s); ΔG = −293 kJ 2Zn(s) + O2(g) → 2ZnO(s); ΔG = −480 kJ Determine the ΔG value for the reaction: 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g).

1. −357 kJ
2. −731 kJ
3. −773 kJ
4. −229 kJ

Correct answer: −773 kJ

Solution

To calculate ΔG for the reaction, we combine the given reactions such that they result in the target reaction. Using Hess's law: ΔG = [ΔG of (2Zn(s) + O2(g) → 2ZnO(s))] + [ΔG of (S2(s) + 2O2(g) → 2SO2(g))] − [ΔG of (2Zn(s) + S2(s) → 2ZnS(s))]. Substituting values: ΔG = (−480) + (−544) − (−293) = −773 kJ.

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