4 KNO3 (s) → 2 K2O (s) + 2 N2 (g) + 5 O2 (g)

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Reaction Type:

Decomposition

Stoichiometry

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Heat Added: kJ
KNO3           Mass: g
K2O            Mass: g
N2             Mass: g  or Gas Volume: L
O2             Mass: g  or Gas Volume: L

Enthalpy of Reaction

[2ΔHf(K2O (s)) + 2ΔHf(N2 (g)) + 5ΔHf(O2 (g))] - [4ΔHf(KNO3 (s))]
[2(-363.17) + 2(0) + 5(0)] - [4(-492.71)] = 1244.5 kJ
1,244.50 kJ     (endothermic)

Entropy Change

[2ΔSf(K2O (s)) + 2ΔSf(N2 (g)) + 5ΔSf(O2 (g))] - [4ΔSf(KNO3 (s))]
[2(94.14) + 2(191.5) + 5(205.03)] - [4(132.93)] = 1064.71 J/K
1,064.71 J/K     (increase in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(K2O (s)) + 2ΔGf(N2 (g)) + 5ΔGf(O2 (g))] - [4ΔGf(KNO3 (s))]
[2(-322.17) + 2(0) + 5(0)] - [4(-393.13)] = 928.18 kJ
928.18 kJ     (nonspontaneous)

From ΔG = ΔH - TΔS:
927.06 kJ     (nonspontaneous)

Equilibrium Constant, K (at 298.15 K)

2.4035388306e-163
This process is not favorable at 25°C.

Reference(s):

Silberberg, Martin S. Chemistry: The molecular Nature of Matter and Change 4th ed.; McGraw-Hill: Boston, MA, 2006; p 128.

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