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Enthalpy of Reaction
[2ΔHf(CaO (s))] - [2ΔHf(Ca (s)) + 1ΔHf(O2 (g))]
[2(-635.13)] - [2(0) + 1(0)] = -1270.26 kJ
-1,270.26 kJ (exothermic)
[2ΔSf(CaO (s))] - [2ΔSf(Ca (s)) + 1ΔSf(O2 (g))]
[2(38.2)] - [2(41.42) + 1(205.03)] = -211.47 J/K
-211.47 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[2ΔGf(CaO (s))] - [2ΔGf(Ca (s)) + 1ΔGf(O2 (g))]
[2(-603.54)] - [2(0) + 1(0)] = -1207.08 kJ
-1,207.08 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-1207.21 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is favorable at 25°C.
Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change 4th ed.; McGraw-Hill: Boston, MA, 2006; p 128.