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Enthalpy of Reaction
[2ΔHf(FeCl3 (s))] - [2ΔHf(Fe (s alpha)) + 3ΔHf(Cl2 (g))]
[2(-399.49)] - [2(0) + 3(0)] = -798.98 kJ
-798.98 kJ (exothermic)
[2ΔSf(FeCl3 (s))] - [2ΔSf(Fe (s alpha)) + 3ΔSf(Cl2 (g))]
[2(142.26)] - [2(27.28) + 3(222.97)] = -438.95 J/K
-438.95 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[2ΔGf(FeCl3 (s))] - [2ΔGf(Fe (s alpha)) + 3ΔGf(Cl2 (g))]
[2(-334.05)] - [2(0) + 3(0)] = -668.1 kJ
-668.10 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-668.11 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is favorable at 25°C.
Kotz, John C., Treichel, Paul, and Weaver, Gabriela. Chemistry & Chemical Reactivity 6th ed.; Thomson Brooks/Cole: Belmont, CA, 2006; p 144.