Let's consider the molecular equation that occurs when aqueous BaCl₂ and aqueous (NH₄)₂SO₄ are mixed in solution to form aqueous NH₄Cl and solid BaSO₄. This is a double displacement reaction.
1 mole of N2 produces 2 moles of NH3 OR... 14 x 2 grams of N2 produces 2(14 +3) grams of NH3 1 gram of N2 produces 34/28 grams of NH3 therefore, 56 grams produce (34/28 )x 56 =68 grams of NH3