Question

Consider the balanced equation.


2HCl + Mg Right arrow. MgCl2 + H2


If 40.0 g of HCl react with an excess of magnesium metal, what is the theoretical yield of hydrogen?
1.11 g
2.22 g
52.2 g
104 g

Answer 1

Moles HCl = 40.0 g / 36.46 g·mol⁻¹ = 1.097 mol.
Stoichiometry: 2 HCl → 1 H2, so moles H2 = 1.097 / 2 = 0.5485 mol.
Mass H2 = 0.5485 mol × 2.016 g·mol⁻¹ = 1.11 g.

Answer: 1.11 g.