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Enthalpy of Reaction
[1ΔHf(ZnI2 (s))] - [1ΔHf(Zn (s)) + 1ΔHf(I2 (s))]
[1(-208.03)] - [1(0) + 1(0)] = -208.03 kJ
-208.03 kJ (exothermic)
[1ΔSf(ZnI2 (s))] - [1ΔSf(Zn (s)) + 1ΔSf(I2 (s))]
[1(161.08)] - [1(41.63) + 1(116.14)] = 3.31 J/K
3.31 J/K (increase in entropy)
Free Energy of Reaction (at 298.15 K)
From ΔGf° values:
[1ΔGf(ZnI2 (s))] - [1ΔGf(Zn (s)) + 1ΔGf(I2 (s))]
[1(-208.95)] - [1(0) + 1(0)] = -208.95 kJ
-208.95 kJ (spontaneous)
From ΔG = ΔH - TΔS:
-209.02 kJ (spontaneous)
Equilibrium Constant, K (at 298.15 K)
This process is favorable at 25°C.
Kotz, John C. and Treichel, Paul. Chemistry & Chemical Reactivity 4th ed.; Thomson Brooks/Cole: Belmont, CA, 1999; pp 161, 173.