SO2 (g) + 1 H2O (ℓ) → H2SO3 (aq)

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Stoichiometry

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SO2            Mass: g  or Gas Volume: L
H2O            Mass: g
H2SO3          Mass: g
Heat Released: kJ

Enthalpy of Reaction

[1ΔHf(H2SO3 (aq))] - [1ΔHf(SO2 (g)) + 1ΔHf(H2O (ℓ))]
[1(-635.55)] - [1(-296.83) + 1(-285.83)] = -52.89 kJ
-52.89 kJ     (exothermic)

Entropy Change

[1ΔSf(H2SO3 (aq))] - [1ΔSf(SO2 (g)) + 1ΔSf(H2O (ℓ))]
[1(-29.29)] - [1(248.11) + 1(69.91)] = -347.31 J/K
-347.31 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[1ΔGf(H2SO3 (aq))] - [1ΔGf(SO2 (g)) + 1ΔGf(H2O (ℓ))]
[1(-486.6)] - [1(-300.19) + 1(-237.18)] = 50.77 kJ
50.77 kJ     (nonspontaneous)

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

Equilibrium Constant, K (at 298.15 K)

1.2734617351e-009
This process is not favorable at 25°C.

Reference(s):

Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 303.

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