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Enthalpy of Reaction
[1ΔHf(NaCl (s))] - [1ΔHf(Na (g)) + 1ΔHf(Cl (g))]
[1(-410.99)] - [1(107.74) + 1(121.29)] = -640.02 kJ
-640.02 kJ (exothermic)
[1ΔSf(NaCl (s))] - [1ΔSf(Na (g)) + 1ΔSf(Cl (g))]
[1(72.38)] - [1(153.59) + 1(165.06)] = -246.27 J/K
-246.27 J/K (decrease in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[1ΔGf(NaCl (s))] - [1ΔGf(Na (g)) + 1ΔGf(Cl (g))]
[1(-384.05)] - [1(77.32) + 1(105.31)] = -566.68 kJ
-566.68 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-566.59 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 305.