Calculate the grams of H2 consumed if 87 g of ammonia is produced according to the reaction: N2 + 3H2 - 2NH3

Answer 1

N₂ + 3H₂ ==> 2NH₃ .. balanced equation

When working problems such as this, we must first convert grams to moles and then at the end, convert back to moles.

molar mass H₂ = 2.02 g / mol

molar mass NH₃ = 17.0 g / mol

moles NH₃ produced = 87 g NH₃ x 1 mol NH₃/ 17.0 g = 5.12 moles NH₃

moles H₂ consumed = 5.12 mols NH₃ x 3 mols H₂ / 2 mols NH₃ = 7.68 mols H₂ consumed

grams H₂ consumed = 7.68 mols H₂ x 2.02 g H₂ / mol = 15.5 g H₂ = 16 g H₂ consumed (2 sig.figs.)