PbS (s) + 2 HCl (aq) → PbCl2 (aq) + H2S (g)

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Stoichiometry

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Heat Added: kJ
PbS            Mass: g
HCl            Mass: g  or Solution Volume: mL of Concentration: mol/L
PbCl2          Mass: g
H2S            Mass: g  or Gas Volume: L

Enthalpy of Reaction

[1ΔHf(PbCl2 (aq)) + 1ΔHf(H2S (g))] - [1ΔHf(PbS (s)) + 2ΔHf(HCl (aq))]
[1(-336) + 1(-20.17)] - [1(-98.32) + 2(-167.15)] = 76.45 kJ
76.45 kJ     (endothermic)

Entropy Change

[1ΔSf(PbCl2 (aq)) + 1ΔSf(H2S (g))] - [1ΔSf(PbS (s)) + 2ΔSf(HCl (aq))]
[1(123.46) + 1(205.77)] - [1(91.34) + 2(56.48)] = 124.93 J/K
124.93 J/K     (increase in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[1ΔGf(PbCl2 (aq)) + 1ΔGf(H2S (g))] - [1ΔGf(PbS (s)) + 2ΔGf(HCl (aq))]
[1(-286.9) + 1(-33.05)] - [1(-96.73) + 2(-131.25)] = 39.28 kJ
39.28 kJ     (nonspontaneous)

From ΔG = ΔH - TΔS:
39.20 kJ     (nonspontaneous)

Equilibrium Constant, K (at 298.15 K)

1.3123776242e-007
This process is not favorable at 25°C.

Reference(s):

Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 185.
Halka, Monica and Nordstrom, Brian. Metals & Metalloids; Infobase Publishing: New York, NY, 2011; pg. 60.

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