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Enthalpy of Reaction
[2ΔHf(I (g))] - [1ΔHf(I2 (g))]
[2(106.84)] - [1(62.44)] = 151.24 kJ
151.24 kJ (endothermic)
[2ΔSf(I (g))] - [1ΔSf(I2 (g))]
[2(180.68)] - [1(260.58)] = 100.78 J/K
100.78 J/K (increase in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[2ΔGf(I (g))] - [1ΔGf(I2 (g))]
[2(70.28)] - [1(19.36)] = 121.2 kJ
121.20 kJ (nonspontaneous)
From ΔG = ΔH - TΔS:
121.19 kJ (nonspontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is not favorable at 25°C.
Atkins, Jones, and Laverman. Chemical Principles 6th ed.; W.H. Freeman and Company: New York, NY, 2013; p 428.