2 PbS (s) + 3 O2 (g) → 2 SO2 (g) + 2 PbO (s red)

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PbS            Mass: g
O2             Mass: g  or Gas Volume: L
SO2            Mass: g  or Gas Volume: L
PbO            Mass: g
Heat Released: kJ

Entropy Change

[2ΔSf(SO2 (g)) + 2ΔSf(PbO (s red))] - [2ΔSf(PbS (s)) + 3ΔSf(O2 (g))]
[2(248.11) + 2(66.53)] - [2(91.34) + 3(205.03)] = -168.49 J/K
-168.49 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(SO2 (g)) + 2ΔGf(PbO (s red))] - [2ΔGf(PbS (s)) + 3ΔGf(O2 (g))]
[2(-300.19) + 2(-189.24)] - [2(-96.73) + 3(0)] = -785.4 kJ
-785.40 kJ     (spontaneous)

From ΔG = ΔH - TΔS:
-784.76 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.
Kotz, John C., Treichel, Paul, and Weaver, Gabriela. Chemistry & Chemical Reactivity 6th ed.; Thomson Brooks/Cole: Belmont, CA, 2006; p 167.
Atkins, Jones, and Laverman. Chemical Principles 6th ed.; W.H. Freeman and Company: New York, NY, 2013; p F95.

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