2 MoS2 (s) + 7 O2 (g) → 2 MoO3 (s) + 4 SO2 (g)

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Stoichiometry

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MoS2           Mass: g
O2             Mass: g  or Gas Volume: L
MoO3           Mass: g
SO2            Mass: g  or Gas Volume: L
Heat Released: kJ

Enthalpy of Reaction

[2ΔHf(MoO3 (s)) + 4ΔHf(SO2 (g))] - [2ΔHf(MoS2 (s)) + 7ΔHf(O2 (g))]
[2(-745.09) + 4(-296.83)] - [2(-235.14) + 7(0)] = -2207.22 kJ
-2,207.22 kJ     (exothermic)

Entropy Change

[2ΔSf(MoO3 (s)) + 4ΔSf(SO2 (g))] - [2ΔSf(MoS2 (s)) + 7ΔSf(O2 (g))]
[2(77.74) + 4(248.11)] - [2(62.59) + 7(205.03)] = -412.47 J/K
-412.47 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(MoO3 (s)) + 4ΔGf(SO2 (g))] - [2ΔGf(MoS2 (s)) + 7ΔGf(O2 (g))]
[2(-668.02) + 4(-300.19)] - [2(-225.94) + 7(0)] = -2084.92 kJ
-2,084.92 kJ     (spontaneous)

From ΔG = ΔH - TΔS:
-2084.24 kJ     (spontaneous)

Equilibrium Constant, K (at 298.15 K)

approaches infinity
This process is favorable at 25°C.

Reference(s):

Zumdahl, Steven and Zumdahl, Susan A. Chemistry 9th ed.; Brooks/Cole: Belmont, CA, 2014; p 131.

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