## 2 H2O (ℓ) → 2 H2 (g) + O2 (g)

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## Stoichiometry

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 Heat Added: kJ H2O            Mass: g H2             Mass: g or Gas Volume: L O2             Mass: g or Gas Volume: L

## 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)

## Entropy Change

[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)

7.7821446653e-084
This process is not favorable at 25°C.

## Reference(s):

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.