2 B5H9 (ℓ) + 12 O2 (g) → 5 B2O3 (s) + 9 H2O (g)

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Stoichiometry

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B5H9           Mass: g
O2             Mass: g  or Gas Volume: L
B2O3           Mass: g
H2O            Mass: g  or Gas Volume: L

Enthalpy of Reaction

[5ΔHf(B2O3 (s)) + 9ΔHf(H2O (g))] - [2ΔHf(B5H9 (ℓ)) + 12ΔHf(O2 (g))]
[5(-1272.77) + 9(-241.82)] - [2(42.68) + 12(0)] = -8625.59 kJ
-8,625.59 kJ     (exothermic)

Entropy Change

[5ΔSf(B2O3 (s)) + 9ΔSf(H2O (g))] - [2ΔSf(B5H9 (ℓ)) + 12ΔSf(O2 (g))]
[5(53.97) + 9(188.72)] - [2(184.22) + 12(205.03)] = -860.47 J/K
-860.47 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[5ΔGf(B2O3 (s)) + 9ΔGf(H2O (g))] - [2ΔGf(B5H9 (ℓ)) + 12ΔGf(O2 (g))]
[5(-1193.7) + 9(-228.59)] - [2(171.67) + 12(0)] = -8369.15 kJ
-8,369.15 kJ     (spontaneous)

From ΔG = ΔH - TΔS:
-8369.04 kJ     (spontaneous)

Equilibrium Constant, K (at 298.15 K)


Reference(s):

Zumdahl, Steven and Zumdahl, Susan A. Chemistry 9th ed.; Brooks/Cole: Belmont, CA, 2014; p 134.

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