I am confused about how to solve it.

Question

What is the total number of moles of NH3(g) produced when 7.5 moles of N2(g) react completely with H2(g)?

Answer 1

First, you must start with a correctly balanced equation for the reaction taking place:

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

Next, we use the stoichiometry of the balanced equation along with dimensional analysis to solve the problem:

7.5 mols N₂ x 2 mols NH₃ / 1 mol N₂ = 15 mols NH₃

This assumes there is excess H₂ present (at least 22.5 moles of H₂ needs to be present, ie 3 x 7.5 mols)

Answer 2

N2 + 3H2 = 2NH3

7.5 moles of N2 upon complete reaction with H2 (assumption is that we have at least 21.5 or higher moles of H2) will produce 15 moles of NH3.