Unit 5: States of Matter
In this unit we explore how matter behaves in terms of the three main phases of matter: solids, liquids, and gases. We investigate gases first, because their properties are described by well-defined equations. Next, we study phase changes, which we describe in terms of a graph known as a phase diagram. We finish this unit with an exploration of the properties of solids.
Completing this unit should take you approximately 15 hours.
Upon successful completion of this unit, you will be able to:
- use kinetic-molecular theory to explain the relationships between gas volume, temperature, number of moles, and pressure;
- perform dimensional analysis conversions for gas law calculations;
- state the ideal gas law;
- describe the motion of particles in liquids and the properties of liquids;
- discuss the process by which liquids can change into a solid or a gas;
- define the characteristics of bonding in ionic compounds;
- interpret phase diagrams; and
- describe and explain the processes of boiling, evaporation, freezing, melting, and sublimation.
5.1: Gases and Gas Laws
Gases are unique because we can use simple relations or equations to describe many of their properties. This works because gas particles take up the entire space of the container they inhabit, move fast, and do not interact with each other. We learn later in the unit that this quality is different from the particles in the liquid or solid phase.
Read this page. Understanding how pressure, temperature, and volume of a gas differ from those of forces that exist within solids and liquids will be fundamental for understanding the upcoming subunits of this course.
Watch these lectures, which introduce ideal gases.
Read this page. Ideal gas laws are laws that apply to gases that behave "ideally", which is when molecules take up no volume and have no attractive forces between one another. In the real world, however, no gas behaves ideally. However, gases are closest to being ideal when they are high-temperature and low-pressure.
Watch this lecture, which discusses partial pressure. A key concept here is that a mixture has a total pressure that is the sum of its component, or partial, pressures.
Read this page, which covers molar properties of gases and partial pressures. After reading this section, you should understand what happens to scuba divers who suffer from nitrogen narcosis, or "the bends".
Read this page. Kinetic molecular theory (KMT) explains the properties of gas molecules and their motion. KMT helps explain how radio waves are transmitted and why the sky is blue.
5.2: Phase Changes
In this section, we discuss phase changes, where one substance changes from one phase of matter to another. We are all familiar with this from everyday life. When an ice cube melts, it changes from solid water to liquid water. When we boil water on the stove and see water vapor form, the water is changing from liquid to gas.
Read this page, which takes a more in-depth look at the properties of liquids, which were introduced previously. Have you ever wondered why all soap bubbles are round? The concepts discussed here will explain.
Watch these videos, which explain how to calculate the amount of energy associated with both temperature changes and phase changes of a particular substance.
Read this page, and focus on the section about the unit cell. Some terms related to symmetry and spectroscopy are introduced here but not covered in detail. More advanced chemistry courses would go into these concepts further.
Read this page, which covers the class of solids that form from ions and the energetics of these compounds.
Read this page, which builds on the concept of the unit cell and describes the packing structures of simple cubic lattices.
- Read this page, which describes the dynamic equilibrium between phases and introduces phase diagrams. There are six different processes by which phases can change from one to another. Some will be familiar to you, such as evaporation or freezing; others might be less familiar, like sublimation and deposition.
Watch these videos to reinforce your understanding of phase diagrams. Although we deal with the three primary states of matter (gases, solids, and liquids) every day, we are often not familiar with their microscopic interactions.
Unit 5 Assessment
Take this assessment to see how well you understood this unit.
- This assessment does not count towards your grade. It is just for practice!
- You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
- You can take this assessment as many times as you want, whenever you want.