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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)
[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)
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.