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Question

The values of ΔG are very important in metallurgy. The ΔG values for the following reactions at 1000 K are given as follows.

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

The ΔG for the reaction 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g) will be

Options

A.−357 kJ
B.−731 kJ
C.−773 kJ
D.−229 kJ

Solution

$\Delta_{r}G = \left\lbrack ( - 480) + ( - 544) \right\rbrack - \left\lbrack ( - 293) \right\rbrack = - 731\text{ kJ}$

$\therefore S_{2} = 2.5 + 4 \times 2 \times 0.7 = 8.1\text{ cal/K.mol}$

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