Convert mass quantities to moles and divide by respective coefficients of balanced equation. The smaller number is the limiting reagent.
Explanation:3H2+N2→2NH3
Example: Assume Given 100 g of each reactant, what's the limiting reagent?
moles of H2=(100g/2gmol−1)=50 moles & Divide by '3' => 16.7
moles of N2=(100g/28gmol−1)=3.57 moles & Divide by '1' => 3.57
The limiting reagent is N2 because after dividing by respective coefficients => 3.57 is smaller than 16.7 and H2 will be in excess; after all N2 is consumed in the reaction.