Chemistry is not just about what reacts, but how much. Stoichiometry gives us the tools to answer quantitative questions: how many grams of product will form, how much of a reagent do we need, and how concentrated is a solution? These are questions that matter in the laboratory, in industry, and in everyday life.

In this chapter, we build up the quantitative framework of chemistry from the ground up. We start with chemical formulae and balanced equations, then introduce relative atomic and molecular masses. From there, we develop the mole concept and the Avogadro constant, which allow us to count particles by weighing them. The chapter then applies these ideas to a wide range of calculations, including reacting masses, gas volumes, solution concentrations, titration data, empirical and molecular formulae, and percentage yield and purity.