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Enthalpy of Reaction
[2ΔHf(H2 (g)) + 1ΔHf(O2 (g))] - [2ΔHf(H2O (ℓ))]
[2(0) + 1(0)] - [2(-285.83)] = 571.66 kJ
571.66 kJ (endothermic)
[2ΔSf(H2 (g)) + 1ΔSf(O2 (g))] - [2ΔSf(H2O (ℓ))]
[2(130.59) + 1(205.03)] - [2(69.91)] = 326.39 J/K
326.39 J/K (increase in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[2ΔGf(H2 (g)) + 1ΔGf(O2 (g))] - [2ΔGf(H2O (ℓ))]
[2(0) + 1(0)] - [2(-237.18)] = 474.36 kJ
474.36 kJ (nonspontaneous)
From ΔG = ΔH - TΔS:
474.35 kJ (nonspontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is not favorable at 25°C.
Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 264.
Halka, Monica and Nordstrom, Brian. Metals & Metalloids; Infobase Publishing: New York, NY, 2011; pg. 66.