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Enthalpy of Reaction
[3ΔHf(S (s rhombic)) + 2ΔHf(H2O (ℓ))] - [2ΔHf(H2S (g)) + 1ΔHf(SO2 (g))]
[3(0) + 2(-285.83)] - [2(-20.17) + 1(-296.83)] = -234.49 kJ
-234.49 kJ (exothermic)
[3ΔSf(S (s rhombic)) + 2ΔSf(H2O (ℓ))] - [2ΔSf(H2S (g)) + 1ΔSf(SO2 (g))]
[3(31.92) + 2(69.91)] - [2(205.77) + 1(248.11)] = -424.07 J/K
-424.07 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[3ΔGf(S (s rhombic)) + 2ΔGf(H2O (ℓ))] - [2ΔGf(H2S (g)) + 1ΔGf(SO2 (g))]
[3(0) + 2(-237.18)] - [2(-33.05) + 1(-300.19)] = -108.07 kJ
-108.07 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-108.05 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is favorable at 25°C.
Atkins, Jones, and Laverman. Chemical Principles 6th ed.; W.H. Freeman and Company: New York, NY, 2013; p F94.