Limiting Reagent

Identifying which reactant runs out first and calculating theoretical yield

Golden Rule: Convert all reactants to moles, divide each by its stoichiometric coefficient. The reactant with the smallest result is the limiting reagent. Calculate yield using only the limiting reagent.

• Step 1: Balance the equation — Write the balanced chemical equation with coefficients for all reactants and products. These coefficients are your mole ratios.
• Step 2: Convert all reactants to moles — For each given reactant, divide the given mass (in grams) by its molar mass (g/mol) to get moles. If given volume of solution, n = C × V.
• Step 3: Divide moles by stoichiometric coefficients — For each reactant, compute n / coefficient. The reactant with the smallest value is the limiting reagent (LR) — it runs out first and limits the amount of product formed.
• Step 4: Calculate theoretical yield from the LR — n(product) = n(LR) × (coefficient of product / coefficient of LR). Convert to grams: m = n × M(product).