The limiting reagent is completely consumed and determines the maximum product. To identify: Method 1: Calculate moles of product from each reactant separately. The reactant giving less product is limiting. Method 2: Divide moles of each reactant by its coefficient. The smallest value identifies the limiting reagent. Example: N2 + 3H2 -> 2NH3. Given 2 mol N2 and 4 mol H2. From N2: 2 x 2 = 4 mol NH3. From H2: 4/3 x 2 = 2.67 mol NH3. H2 gives less product — H2 is limiting. NH3 produced = 2.67 mol. Excess N2 = 2 - 4/3 = 0.67 mol. Always check both reactants — never assume.