Question

Combine the two reactions and find Delta G.

Rxn 1: H₂S + 1/2O₂ ---> S^o + H₂O

Rxn 2: S^o + 3/2O₂ + H₂O ---> SO₄^2- + 2H+

H2O = -237.17 kj/mol

H2O2 = -134.1 kj/mol

H+ = -39.87 kj/mol

SO4(2-) = -744.6 kj/mol

H2S = -27.87 kj/mol

Answer 1

Rxn 1: H₂S + 1/2O₂ ---> SO + H₂O

Rxn 2: SO + 3/2O₂ + H₂O ---> SO₄^2- + 2H⁺

Combined reaction: H₂S + 2O₂ ---> SO₄^2- + 2H⁺

ΔG°reaction =∑ c_products ΔG° (products)- ∑ c_reactants ΔG° (reactants)

We have :
Like ΔHf°,ΔGf° = 0 for an element in its standard state:
Example: ΔGf°(O₂(g)) = 0

H2O = -237.17 kj/mol

H2O2 = -134.1 kj/mol

H+ = -39.87 kj/mol

SO4(2-) = -744.6 kj/mol

H2S = -27.87 kj/mol

Plug all into the above;

ΔG°reaction = {(-744.6 kj/mol) + 2 x (-39.87 kj/mol)} - {(-27.87 kj/mol) + 2x (0)} = - 796.47 kj/mol