N2O4 (g) → 2 NO2 (g)

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Heat Added: kJ
N2O4           Mass: g  or Gas Volume: L
NO2            Mass: g  or Gas Volume: L

Enthalpy of Reaction

[2ΔHf(NO2 (g))] - [1ΔHf(N2O4 (g))]
[2(33.18)] - [1(9.16)] = 57.2 kJ
57.20 kJ     (endothermic)

Entropy Change

[2ΔSf(NO2 (g))] - [1ΔSf(N2O4 (g))]
[2(239.95)] - [1(304.18)] = 175.72 J/K
175.72 J/K     (increase in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(NO2 (g))] - [1ΔGf(N2O4 (g))]
[2(51.3)] - [1(97.82)] = 4.78 kJ
4.78 kJ     (nonspontaneous)

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

Equilibrium Constant, K (at 298.15 K)

This process is close to or at equilibrium at 25°C.


Atkins, Jones, and Laverman. Chemical Principles 6th ed.; W.H. Freeman and Company: New York, NY, 2013; p 428.

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