How do you do this step by step chemistry

How many moles of hydrogen are needed to completely react with 12 grams of nitrogen

N2+3H2-->2NH3

check that the equation is properly balanced

N2 + 3H2 ----> 2NH3

moles N2 = mass / molar mass
= 12 g / 28.02 g/mol
= 0.42827 mol

The balanced equation tells you that 1 mole N2 reacts with 3 moles H2
So moles H2 needed = 3 x moles N2
= 3 x 0.42827 mol
= 1.285 mol
= 1.3 mol (2 sig figs)