Firstly, a balanced equation has to be written for the production of ammonia (NH₃) from hydrogen gas (H₂) and nitrogen gas (N₂):
N₂ + 3H₂ → 2NH₃
Now, the mole ratio of N₂ : NH₃ is 1 : 2 based on the coefficients of the balanced equation.
If the moles of N₂ = 2.5 moles
then the moles of NH₃ produced = 2.5 mol × 2
= 5 mol
Thus, the moles of ammonia produced when 2.5 mol of nitrogen gas is combined with excess hydrogen gas is 5 mol.
