Iron can reduce sulfuric acid to produce solid sulfur. It can also reduce sulfuric acid to produce sulfur dioxide: 

(i) 3 Fe(s) + SO₄²⁻(aq) + 8 H⁺(aq) → S(s) + 4 H₂O(l) + 3 Fe²⁺(aq)           E° = 0.49 V

(ii) Fe(s) + SO₄²⁻(aq)  + 4 H⁺(aq) → SO₂(g) + 2 H₂O(l) + Fe²⁺(aq)           E° = 0.28 V

What is the potential for reaction (i) if there are 0.15 M Fe²⁺ and 0.20 M H₂SO₄? What is the potential for reaction (ii) if there are 0.15 M Fe²⁺, 0.20 M H₂SO₄, and 1.0 atm SO₂ gas? Which of the two reactions has a greater thermodynamic tendency if the concentration of H₂SO₄ is 0.15 M? (Assume that H₂SO₄ fully dissociates.)