Consider 4NH3 + 3O2=2N2 +6 H2O.How many mols of NH3 will react with 0.40 mols of O2?How many mols of O2 must react to form 0.40 mols of H20?

4NH₃ + 3O₂ → 2N₂ + 6H₂O

Mole ratio NH₃ : O₂ = 4 : 3
No. of moles of NH₃ that will react with 0.40 mol of O₂ = (0.40 mol) × (4/3) = 0.53 mol

Mole ratio O₂ : H₂O = 3 : 6 = 1 : 2
No. of moles of O₂ needed to form 0.40 mol of H₂O = (0.40 mol) × (1/2) = 0.2 mol

The molar ratios are 4:3::2:6
So by equivalence
(4 x 0.4/3) : 0.40 = 0.5333... : 0.4

Again by equivalence
3 : 6 :: 1 : 2 :: 0.2: 0.4

...
look at the coefficients in the balanced equation
these give mole ratios
so
mol NH3 / 0.40 mol O2 = 4NH3 / 3 O2
mol NH3 = 0.53 mol

mol O2 / 0.40 mol H2O = 3O2 / 6H20
mol O2 = 0.20 mol

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