8.4 The Kinetic Molecular Theory and Real Gas Behavior Warm Up Assume the box shown here has a volume of 22.4 L and exists under standard temperature and pressure (STP) conditions. Draw a molecular representation of oxygen gas filling the box. List three ways in which your drawing fails to represent the actual situation.
A Model for Gases — The Kinetic Molecular Theory
Your first introduction to chemistry in elementary school may have been a study of the kinetic molecular theory of matter (KMT). This theory states that matter is composed of particles such as molecules, atoms, or ions in continuous motion (Figure 8.4.1). In the solid state, the particles are close together and only vibrate. In a liquid, the particles are farther apart and move around. In a gas, the particles are much farther apart and move around freely in a random fashion. A mole of gas occupies 22.4 L, while a mole of most liquids has a volume of only 18 mL. In this section, we will take a closer look at how this theory applies to gases.
Figure 8.4.1 The particles of a solid are packed tightly together. Liquid particles are farther apart and can
move freely. A gas is virtually impossible to represent because the particles are no more than tiny points in space with less than 0.01% of the volume occupied by the actual gas molecules. There is a regular distribution of speeds for the molecules. Some are hardly moving while others have far more energy and are moving very quickly.
When we use KMT to explain the behavior of gases, we make a number of assumptions about the size of the molecules, the way they behave, and what does and does not occur during particle collisions. Such assumptions are included in the postulates of the kinetic molecular theory.
490 Chapter 8 Gases
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