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Enthalpy of Reaction
[2ΔHf(SO3 (g))] - [2ΔHf(S (s rhombic)) + 3ΔHf(O2 (g))]
[2(-395.72)] - [2(0) + 3(0)] = -791.44 kJ
-791.44 kJ (exothermic)
[2ΔSf(SO3 (g))] - [2ΔSf(S (s rhombic)) + 3ΔSf(O2 (g))]
[2(256.65)] - [2(31.92) + 3(205.03)] = -165.63 J/K
-165.63 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[2ΔGf(SO3 (g))] - [2ΔGf(S (s rhombic)) + 3ΔGf(O2 (g))]
[2(-371.08)] - [2(0) + 3(0)] = -742.16 kJ
-742.16 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-742.06 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is favorable at 25°C.
Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 205.