For N2 + 3H2 -> 2NH3, if 10.0 mol N2 reacts with 20.0 mol H2, identify the limiting reactant and find the theoretical amount of NH3 produced.

Compare how much NH3 each reactant can make.
From N2: 10.0 mol N2 * (2 mol NH3 / 1 mol N2) = 20.0 mol NH3
From H2: 20.0 mol H2 * (2 mol NH3 / 3 mol H2) = 13.3 mol NH3
H2 produces less NH3, so H2 is limiting.
The theoretical amount is 13.3 mol NH3.