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Enthalpy of Reaction
[2ΔHf(H2O (ℓ))] - [2ΔHf(H2 (g)) + 1ΔHf(O2 (g))]
[2(-285.83)] - [2(0) + 1(0)] = -571.66 kJ
-571.66 kJ (exothermic)
[2ΔSf(H2O (ℓ))] - [2ΔSf(H2 (g)) + 1ΔSf(O2 (g))]
[2(69.91)] - [2(130.59) + 1(205.03)] = -326.39 J/K
-326.39 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[2ΔGf(H2O (ℓ))] - [2ΔGf(H2 (g)) + 1ΔGf(O2 (g))]
[2(-237.18)] - [2(0) + 1(0)] = -474.36 kJ
-474.36 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-474.35 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; pp 223-4.