Question

What mass of nitrogen gas is required to react completely with 2.79 g of hydrogen gas to produce ammonia?

Answer 1

The balanced equation for the formation of ammonia is as follows
N₂ + 3H₂ ---> 2NH₃
stoichiometry of H₂ to N₂ is 3:1
number of H₂ moles reacted - 2.79 g / 2 g/mol  = 1.40 mol 
if 3 mol of H₂ reacts with 1 mol of N₂
then 1.40 mol of H₂ reacts with  - 1.40/3 = 0.467 mol of N₂
mass of N₂ required - 0.467 mol x 28 g/mol = 13.1 g
mass of N₂ formed is 13.1 g