To determine the limiting reactant, we first calculate the number of moles of the reactant.
7.00 g H2 ( 1 mol / 2.02 g ) = 3.47 mol H2
70.00 g N2 ( 1 mol / 28.02 g) = 2.50 mol N2
From the balanced reaction, we see that there is a 3 is to 1 ratio of the reactants. So, for every 3 moles of H2 we need 1 mole of N2. Given the amount of reactant, for 2.50 moles of N2 we need 7.5 moles of H2 which obviously we have a lesser amount. Hydrogen is the limiting reactant.
