This chapter describes how we model matter in the gas phase. This is important since many of the Thermodynamic models which we study are based on the results of the behvior of gases as modeled by things like the Ideal Gas Law, or other models for real gases, such as the van der Waals Law.
In this chapter, we will review Empirical Gas Laws, Avogadro's Law, and the Ideal Gas Law. Next we will discuss how a kinetic molecular model leads to ideal gas behavior. And finally, we will discuss how real gases deviate from ideal behavior, leading to such curious properties as Critical behavior.
Students should understand the relationships between pressure, volume, temperature, and amount of gas as described by the empirical gas laws and the Ideal Gas Law. These equations provide the foundation for predicting and modeling the behavior of gases in chemical systems.
The Kinetic Molecular Theory explains gas behavior in terms of molecular motion and collisions. Students should understand the theory's postulates and how they lead to a microscopic expression for gas pressure.
Molecules in a gas possess a distribution of speeds rather than a single velocity. Students should be able to interpret Maxwell-Boltzmann distributions and relate molecular speeds to temperature and molecular mass.
Molecular collisions govern diffusion, effusion, and chemical reactivity. Students should be able to describe collision frequencies, mean free paths, and other transport properties using the Kinetic Molecular Theory.
Real gases deviate from ideal behavior because molecules occupy finite volume and interact with one another. Students should understand how equations of state and related concepts such as the Boyle Temperature, Critical Behavior, and the Principle of Corresponding States describe these deviations.