Thermodynamics tells you what reactions can happen, but not how fast they will happen. In fact, some reactions are so slow that they are never actually observed, even though they are thermodynamically allowed. Other reactions are stunningly fast. In this part of the book, we will discuss the factors that affect rates of reaction, and consider some basic theories that can be used to rationalize them. This chapter introduces a few definitions and ideas that we will need in our study of kinetics.

The business of kinetics

Chemical kinetics is the study of the rates of chemical reactions or, to put it in simpler language, of the speeds of chemical reactions. There are many different questions one can ask about how fast reactions go, and many different approaches one can take to answering these questions. Roughly though, we can break down the field into two major branches:

1. (1) Phenomenological kinetics: this is the part of kinetics that is concerned with measuring rates of reactions and with the relationship between rates and chemical mechanisms.

2. (2) Kinetic theory and dynamics: this field focuses on the relationship between rates of reactions and events on a molecular scale. In the best cases, we are able to predict a reaction mechanism and the rates of the reactions that make up that mechanism. More commonly, kinetic theory or dynamics let us relate molecular properties to observed reaction rates. Kinetic theory and dynamics are attempts to answer questions about why the rate of a reaction has a particular value, rather than just taking the rates as quantities determined by experiment, as we do in phenomenological kinetics.