This semester begins with the introduction of the mole. This important concept will be used during the remainder of the year as the basis for many calculations involving chemical reactions, solutions, and gases. In the units on thermochemistry and chemical kinetics, you will learn how energy is absorbed and given off during chemical reactions and how energy, and factors affect the rates of reactions. The study of reaction rates will lead you into the study of chemical equilibrium. In this semester, you will also study electrochemistry, from batteries to electroplating. And you will learn about acids, bases and salts. Unit 15 is a brief study of the atomic nucleus, which your teacher may introduce at any time during the year.