The next seven chapters will be devoted to using numbers in chemistry and making it exact. This will lead to an understanding of why substances react, why they appear to react only so far and no farther, and why they do so rapidly or slowly. One of the practical triumphs of chemistry is the ability to control the rates and course of chemical processes, to produce useful substances and energy. The advantages in industrial synthesis are obvious; but the advantages in biosynthesis are no less important.

These next seven chapters are an introduction to some aspects of physical chemistry, although quantum theory normally is included also as a part of physical chemistry. Chapters 18 through 21 introduce the subject of organic chemistry, and Chapters 22 through 26 bring us to biochemistry and the evolution of life. One should not pay too much attention to these categories, however, because the most active research today is being done in borderline areas that do not fall easily into any category. It is the overall view of the unity of chemistry that is important.