Question

If given 0.45 moles of N2 react with an excess of hydrogen, how many moles of NH3 are produced

Answer 1

First you write the balanced reactions
n2 + 3H2 -> 2NH3

Answer 2

now you use stoichiometry
.45 mol n2 * 2 mol NH3/1 mol n2 = .9 mols of NH3