Consider 2 H2S + SO2 -> 3 S + 2 H2O.How many moles of H2S must react to form 4.0 moles of S?How many moles of SO2 react to form 4 mol of H20?

2H₂S + SO₂ → 3S + 2H₂O

Mole ratio H₂S : S = 2 : 3
No. of moles of H₂S needed to form 4.0 mol of S = (4.0 mol) × (2/3) = 2.7 mol

Mole ratio SO₂ : H₂O = 1 : 2
No. of moles of SO₂ needed to form 4 mol of H₂O = (4 mol) × (1/2) = 2 mol