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Enthalpy of Reaction
[2ΔHf(Al2O3 (s alpha-corundum))] - [4ΔHf(Al (s)) + 3ΔHf(O2 (g))]
[2(-1675.27)] - [4(0) + 3(0)] = -3350.54 kJ
-3,350.54 kJ (exothermic)
[2ΔSf(Al2O3 (s alpha-corundum))] - [4ΔSf(Al (s)) + 3ΔSf(O2 (g))]
[2(50.92)] - [4(28.33) + 3(205.03)] = -626.57 J/K
-626.57 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[2ΔGf(Al2O3 (s alpha-corundum))] - [4ΔGf(Al (s)) + 3ΔGf(O2 (g))]
[2(-1581.97)] - [4(0) + 3(0)] = -3163.94 kJ
-3,163.94 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-3163.73 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is favorable at 25°C.
Kotz, John C., Treichel, Paul, and Weaver, Gabriela. Chemistry & Chemical Reactivity 6th ed.; Thomson Brooks/Cole: Belmont, CA, 2006; p 166.