4 Cr (s) + 3 O2 (g) → 2 Cr2O3 (s)

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Reaction Type:

Synthesis

Stoichiometry

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Cr             Mass: g
O2             Mass: g  or Gas Volume: L
Cr2O3          Mass: g

Enthalpy of Reaction

[2ΔHf(Cr2O3 (s))] - [4ΔHf(Cr (s)) + 3ΔHf(O2 (g))]
[2(-1134.7)] - [4(0) + 3(0)] = -2269.4 kJ
-2,269.40 kJ     (exothermic)

Entropy Change

[2ΔSf(Cr2O3 (s))] - [4ΔSf(Cr (s)) + 3ΔSf(O2 (g))]
[2(81.17)] - [4(23.62) + 3(205.03)] = -547.23 J/K
-547.23 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(Cr2O3 (s))] - [4ΔGf(Cr (s)) + 3ΔGf(O2 (g))]
[2(-1053.11)] - [4(0) + 3(0)] = -2106.22 kJ
-2,106.22 kJ     (spontaneous)

From ΔG = ΔH - TΔS:
-2106.24 kJ     (spontaneous)

Equilibrium Constant, K (at 298.15 K)

approaches infinity
This process is favorable at 25°C.

Reference(s):

Kotz, John C. and Treichel, Paul. Chemistry & Chemical Reactivity 4th ed.; Thomson Brooks/Cole: Belmont, CA, 1999; p 173.
Kotz, John C., Treichel, Paul, and Weaver, Gabriela. Chemistry & Chemical Reactivity 6th ed.; Thomson Brooks/Cole: Belmont, CA, 2006; p 166.

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