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Enthalpy of Reaction
[1ΔHf(C2H6 (g ethane))] - [1ΔHf(C2H4 (g ethylene)) + 1ΔHf(H2 (g))]
[1(-84.68)] - [1(52.3) + 1(0)] = -136.98 kJ
-136.98 kJ (exothermic)
[1ΔSf(C2H6 (g ethane))] - [1ΔSf(C2H4 (g ethylene)) + 1ΔSf(H2 (g))]
[1(229.12)] - [1(219.2) + 1(130.59)] = -120.67 J/K
-120.67 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[1ΔGf(C2H6 (g ethane))] - [1ΔGf(C2H4 (g ethylene)) + 1ΔGf(H2 (g))]
[1(-32.8)] - [1(68.24) + 1(0)] = -101.04 kJ
-101.04 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-101.00 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is favorable at 25°C.
Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 224.