Question

Mg + 2HCl 🡪 MgCl2 + H2

How many grams of HCl are consumed by the reaction of 2.50 moles of magnesium?


What is the mass in grams of H2 gas when 4.0 moles of HCl is added to the reaction?

Answer 1

Balanced: Mg + 2 HCl → MgCl2 + H2

1) Moles HCl needed for 2.50 mol Mg:
- Stoichiometry: 2 mol HCl per 1 mol Mg → moles HCl = 2 × 2.50 = 5.00 mol
- Mass HCl = 5.00 mol × 36.46 g/mol = 182.3 g ≈ 182 g (3 s.f.)

2) Mass of H2 when 4.0 mol HCl is reacted:
- If Mg is in excess (or if 4.0 mol HCl is the limiting reactant): 2 mol HCl → 1 mol H2, so moles H2 = 4.0 × (1/2) = 2.0 mol
- Mass H2 = 2.0 mol × 2.016 g/mol = 4.03 g ≈ 4.0 g (2 s.f.)

(If you meant 4.0 mol HCl added to 2.50 mol Mg, HCl is limiting and the result is the same: 2.0 mol H2 → 4.03 g.)