So far, we have talked about chemical reactions in terms of individual atoms and molecules. Although this works, most of the reactions occurring around us involve much larger amounts of chemicals. Even a tiny sample of a substance will contain millions, billions, or a hundred billion billions of atoms and molecules. How do we compare amounts of substances to each other in chemical terms when it is so difficult to count to a hundred billion billion? Actually, there are ways to do this, which we will explore in this chapter. In doing so, we will increase our understanding of stoichiometry, which is the study of the numerical relationships between the reactants and the products in a balanced chemical reaction. 6.1: The Mole A mole is \(6.022 \times 10^{23}\) things. 6.2: Atomic and Molar Masses The mass of moles of atoms and molecules is expressed in units of grams. 6.3: Mole-Mass Conversions It is possible to convert between moles of material and mass of material. 6.4: Mole-Mole Relationships in Chemical Reactions The balanced chemical reaction can be used to determine molar relationships between substances. 6.5: Mole-Mass and Mass-Mass Problems A balanced chemical equation can be used to relate masses or moles of different substances in a reaction. 6.6: Chapter Summary To ensure that you understand the material in this chapter, you should review the meanings of the following bold terms in the following summary and ask yourself how they relate to the topics in the chapter. 6.E: Exercise Select problems and solution.