Read the contents of the problem, and write down the given information. For example, the problem may state that 0.05 liters of 0.05 M NH3 reacts with 0.06 L of 0.5 M H2SO4 to produce (NH4)2SO4.
Write the chemical equation. The chemical equation shows the details of the reaction. For example, when NH3 reacts with H2SO4, the chemical equation is
2NH3 + H2SO4 gives you (NH4)2SO4.
Determine the number of moles of each of the reactants. In most problems were you are given the volume, you are also given information about the type of solution. For example, both the NH3 and the H2SO4 are 0.5 M solutions. The molarity, M, is the number of moles of solute per liters of solution. The equation of the molarity is M = m / V, where m is the number of moles and V is the volume. Solving for the number of moles gives you m = M x V. For NH3, m = (0.5)(0.05) = 0.025 moles. For H2SO4, m = (0.5)(0.06) = 0.03 moles.
Calculate the number of moles of product produced. You can use dimensional analysis for this process. For NH3, the first ratio is 0.025 moles NH3 over 1, and the second ratio is 1 mole of (NH4)2SO4 over 2 moles NH3. Multiplying these ratios gives you 0.0125 moles of (NH4)2SO4. For H2SO4, the first ratio is 0.03 moles of H2SO4 over 1 and the second ratio is 1 mole of (NH4)2SO4 over 1 mole of H2SO4. Multiplying these ratios gives you 0.03 moles of H2SO4.
Compare the moles of product that each reactant produces. The NH3 produces 0.0125 moles of product, whereas the H2SO4 produces 0.03 moles of product. Since the NH3 produces the smaller amount of product, the NH3 is the limiting reactant.