## 4 FeS2 (s pyrite) + 2 H2O (ℓ) + 15 O2 (g) → 2 Fe2(SO4)3 (aq) + 2 H2SO4 (aq)

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## Stoichiometry

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 FeS2           Mass: g H2O            Mass: g O2             Mass: g or Gas Volume: L Fe2(SO4)3      Mass: g H2SO4          Mass: g Heat Released: kJ

## Enthalpy of Reaction

[2ΔHf(Fe2(SO4)3 (aq)) + 2ΔHf(H2SO4 (aq))] - [4ΔHf(FeS2 (s pyrite)) + 2ΔHf(H2O (ℓ)) + 15ΔHf(O2 (g))]
[2(-2824.87) + 2(-909.27)] - [4(-178.24) + 2(-285.83) + 15(0)] = -6183.66 kJ
-6,183.66 kJ     (exothermic)

## Entropy Change

[2ΔSf(Fe2(SO4)3 (aq)) + 2ΔSf(H2SO4 (aq))] - [4ΔSf(FeS2 (s pyrite)) + 2ΔSf(H2O (ℓ)) + 15ΔSf(O2 (g))]
[2(-571.54) + 2(20.08)] - [4(52.93) + 2(69.91) + 15(205.03)] = -4529.91 J/K
-4,529.91 J/K     (decrease in entropy)

## Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(Fe2(SO4)3 (aq)) + 2ΔGf(H2SO4 (aq))] - [4ΔGf(FeS2 (s pyrite)) + 2ΔGf(H2O (ℓ)) + 15ΔGf(O2 (g))]
[2(-2243.09) + 2(-744.63)] - [4(-166.94) + 2(-237.18) + 15(0)] = -4833.32 kJ
-4,833.32 kJ     (spontaneous)

From ΔG = ΔH - TΔS:
-4833.07 kJ     (spontaneous)

## Equilibrium Constant, K (at 298.15 K)

approaches infinity
This process is favorable at 25°C.

## Reference(s):

Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 216.