Solids, Liquids, and Gases
When you put water in ice cube trays and set them in the freezer, you are expecting a change in state. In a short while, the liquid water will become a solid—ice. Matter usually can be found in three different states: solid, liquid, or gas.
A solid has a definite shape and volume. Although the individual particles vibrate back and forth in a solid, the particles stay in the same position. If you add heat to the solid, it will melt and become a liquid. If you continue to add more heat, at a certain temperature, the liquid will vaporize and become a gas.
Look around your classroom. Write down the examples of solids, liquids, and gases that can be found there. Which category has the most items?
Properties of a Gas
Gas particles are in constant motion, colliding with each other and with the walls of their container. A gas will expand to fill the size and shape of its container. Read about three properties of a gas.
Volume: The volume of a gas will be the volume of its container.
Temperature: The temperature of a gas is a measure of the average kinetic energy of the moving particles. If the particles are moving faster, their energy will be greater and the temperature will be higher.
Pressure: The pressure of a gas is the force of its outward push divided by the area of the walls of the container.
These three properties of gases—volume, temperature and pressure—are all related. Learn more by investigating two gas laws and answering questions about them.
The Gas Laws
In this diagram you can see that more mass is added to the top of the plunger at each stage. The more mass, the more the gas is compressed. The same number of gas particles are trapped in an increasingly smaller space, which increases the pressure of the gas on the walls of the container. According to Boyle's law, when the pressure of a gas is increased at constant temperature its volume decreases. When the pressure of a gas is decreased, its volume increases.
Charles's law explains how the temperature of a gas affects its volume.
Study the diagrams for Boyle's law and Charles's law. Then fill in the table and answer the questions below.
Behavior of Gases
- What would happen to a balloon if you filled it with warm air and set it in a freezer for an hour?
- What would happen to a balloon if you filled it with cooler air and then placed it in the hot sun for an hour?
Predict the outcome, then try this at home. Share your results with your classmates.
Further Exploration
Gases are challenging to understand because we generally cannot see them. Here is a gas model from the Exploratorium to try out. Then try creating your own experiment to model the behavior of gases.