Stoichiometry
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Enthalpy of Reaction
[4ΔHf(NO2 (g)) + 1ΔHf(O2 (g))] - [2ΔHf(N2O5 (s))]
[4(33.18) + 1(0)] - [2(11.3)] = 110.12 kJ
110.12 kJ (endothermic)
Entropy Change
[4ΔSf(NO2 (g)) + 1ΔSf(O2 (g))] - [2ΔSf(N2O5 (s))]
[4(239.95) + 1(205.03)] - [2(347.19)] = 470.45 J/K
470.45 J/K (increase in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[4ΔGf(NO2 (g)) + 1ΔGf(O2 (g))] - [2ΔGf(N2O5 (s))]
[4(51.3) + 1(0)] - [2(117.7)] = -30.2 kJ
-30.20 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-30.14 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
195481.42305
This process is favorable at 25°C.
Reference(s):
Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 135.