SiCl4 (ℓ) + 2 Mg (s) → Si (s) + 2 MgCl2 (s)

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Stoichiometry

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SiCl4          Mass: g
Mg             Mass: g
Si             Mass: g
MgCl2          Mass: g
Heat Released: kJ

Enthalpy of Reaction

[1ΔHf(Si (s)) + 2ΔHf(MgCl2 (s))] - [1ΔHf(SiCl4 (ℓ)) + 2ΔHf(Mg (s))]
[1(0) + 2(-641.62)] - [1(-687.01) + 2(0)] = -596.23 kJ
-596.23 kJ     (exothermic)

Entropy Change

[1ΔSf(Si (s)) + 2ΔSf(MgCl2 (s))] - [1ΔSf(SiCl4 (ℓ)) + 2ΔSf(Mg (s))]
[1(18.83) + 2(89.62)] - [1(239.74) + 2(32.69)] = -107.05 J/K
-107.05 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[1ΔGf(Si (s)) + 2ΔGf(MgCl2 (s))] - [1ΔGf(SiCl4 (ℓ)) + 2ΔGf(Mg (s))]
[1(0) + 2(-592.12)] - [1(619.9) + 2(0)] = -1804.14 kJ
-1,804.14 kJ     (spontaneous)

From ΔG = ΔH - TΔS:
-564.31 kJ     (spontaneous)

Equilibrium Constant, K (at 298.15 K)

approaches infinity
This process is favorable at 25°C.

Reference(s):

Kotz, John C. and Treichel, Paul. Chemistry & Chemical Reactivity 4th ed.; Thomson Brooks/Cole: Belmont, CA, 1999; p 158.

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