Stoichiometry

Mole ratios, limiting reagents, and theoretical yield

Stoichiometry uses the coefficients of a balanced chemical equation to relate amounts of reactants and products. The mole ratio (coefficient ratio) converts between moles of different substances. The limiting reagent is the reactant that runs out first, determining the maximum product (theoretical yield). The excess reagent has leftover moles after the reaction completes. For a reaction aA + bB → cC: if (moles A)/a < (moles B)/b, then A is limiting. Theoretical moles of C = (moles of limiting reagent) × (c/a or c/b). Conservation of mass requires that total atoms of each element are equal on both sides.