3 H2(g) + N2(g)  2 NH3(g)

• The balanced equation shows that 3 H2 molecules react with 1 N2 molecule to form 2 NH3 molecules.
• We can express these relationships as ratios.

3 H2 molecules : 1 N2 molecule : 2 NH3 molecules

• Since we do not ordinarily deal with individual molecules, we can express the same ratios in moles.

3 mol H2 : 1 mol N2 : 2 mol NH3