2.1 Introduction

As is well-known, there are three normal states of matter.^2.1 These are solids, liquids, and gases. Typically solids have both a fixed volume and a fixed shape.^2.2 Liquids have a definite volume but adopt the shape of their container. Gases have neither a shape nor a volume but depend on their container to define both.

Theoretical physical chemists and physicists often try to model these states on an atomic level. Solids have the advantage of being regular in molecular arrangement, which can simplify their description. Gases have the advantage of being totally chaotic, which also can simplify their description. Liquids, on the other hand are famously difficult to deal with on a molecular level.

Of all of these gases are the easiest to apply thermodynamics to. Thus it is with gases that we shall start.