Ammonia is manufactured from the reaction between nitrogen and hydrogen.
N2 + 3H2 ⇌ 2NH3
What is the maximum mass of ammonia that can be obtained from a mixture of 56g of
nitrogen with 9 g of hydrogen? (Relative atomic masses: H = 1; N = 14.)

Answer:

9) B

n(H₂) = 9/2 = 4.5 moles
n(N₂) = 56/28 = 2 moles

Ratio of H₂:NH₃ = 3:2
4.5 moles of Hydrogen reacts with 3 moles of Ammonia

We then use the formula:
moles = mass/Mr
moles = 3
mass = unknown
Mr = 14 + 3 = 17

moles = m/Mr
m = moles x Mr = 3 x 17 = 51 grams