First, write the balanced chemical equation involved. Since the reaction is synthesis of NH3, N2 + 3 H2 -> 2 NH3.
Since N2 is excess, H2 is limiting and we, therefore, use its moles to determine the amount of NH3 produced. In the equation, there are 2 moles of NH3 produced over 3 moles of H2 reactant. Thus, we use this ratio:
12.0 mol H2 ( 2 mol NH3 / 3 mol H2 ) = ____ mol NH3
