If N2 + 3H2 -> 2NH 3, how much H2 is needed to react with 15g of N2?

Answer 1

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

From the balanced equation we see that it takes 3 MOLES of H₂ to react with each 1 MOLE of N₂. (Note: we work in moles, not grams, for these types of stoichiometry problems). So we will first find out how many moles of N₂ we have in 15 g of N₂, and then find moles of H₂ needed (3 x). That will be our answer in moles. If we want to convert to grams, we will do that at the end.

Moles of N₂ present = 15 g N₂ x 1 mole N₂ / 28 g = 0.536 moles N₂

Moles of H₂ needed = 0.536 moles N₂ x 3 moles H₂ / 1 mol N₂ = 1.6 moles H₂ needed (answer)*

Grams of H₂ needed = 1.61 moles H₂ x 2 g H₂ / mole = 3.2 grams of H₂ needed (answer)*

*Answers given to 2 significant figures.