12.1 The Arithmetic of Equations

• A balanced chemical equation provides the same kind of quantitative information that a recipe does.
• Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction.
• A balanced chemical equation can be interpreted in terms of different quantities, including numbers of atoms, molecules, or moles; mass; and volume.
• Mass and atoms are conserved in every chemical reaction.

12.2 Chemical Calculations

• In chemical calculations, mole ratios are used to convert between moles of reactant and moles of product, between moles of reactants, or between moles of products.
• In a typical stoichiometric problem, the given quantity is first converted to moles. Then the mole ratio from the balanced equation is used to calculate the moles of the wanted substance. Finally, the moles are converted to any other unit of measurement related to the unit mole.

12.3 Limiting Reagent and Percent Yield

• In a chemical reaction, an insufficient quantity of any of the reactants will limit the amount of product that forms.
• The percent yield is a measure of the efficiency of a reaction performed in the laboratory.