1. Section 4: Behavior of Gases
Preview
Key Ideas
Bellringer
Properties of Gases
Gas Laws
Math Skills

2. Key Ideas
What are some properties of gases?
How can you predict the effects of pressure, temperature, and volume changes on gases?

3. Bellringer
The pressure of gas depends on how frequently the particles of gas strike the sides of the container holding the gas. Use your experience and, after examining each of the pairs of drawings shown below, decide whether you think the pressure of the contained gas has increased, decreased, or remained unchanged. Choose the correct answer.
1. The gas in the cylinder of an automatic engine undergoes the change shown below. Does the pressure of the gas
a. increase?
b. decrease?
c. remain unchanged?
EDIT: Check against final.

4. Bellringer, continued
2. The gas in the toy balloon expands outward, as shown below. After this expansion, does the pressure of the gas
a. increase?
b. decrease?
c. remain unchanged?
3. The temperature of the water vapor in the pressure cooker increases. Does the pressure of the gas
a. increase?
b. decrease?
c. remain unchanged?
EDIT: Check against final.

5. Properties of Gases What are some properties of gases?
Gases expand to fill their containers. They spread out easily and mix with one another. They have low densities and are compressible. Unlike solids and liquids, gases are mostly empty space. Also, gases exert pressure on their containers.

6. Visual Concept: Properties of Gases

7. Gas Laws
How can you predict the effects of pressure, temperature, and volume changes on gases?
The gas laws will help you understand and predict the behavior of gases in specific situations.
gas laws: the laws that state the mathematical relationships between the volume, temperature, pressure, and quantity of a gas

8. Boyle’s law relates the pressure of a gas to its volume.
Gas Laws
Boyle’s law relates the pressure of a gas to its volume.
Boyle’s law: For a fixed amount of gas at a constant temperature, the volume of a gas increases as the gas’s pressure decreases. Likewise, the volume of a gas decreases as the gas’s pressure increases.
P1V1 = P2V2

9. Visual Concept: Boyle’s Law

10. Math Skills Boyle’s Law
The gas in a balloon has a volume of 7.5 L at 100 kPa. The balloon is released into the atmosphere, and the gas expands to a volume of 11 L. Assuming a constant temperature, what is the pressure on the balloon at the new volume?
1. List the given and unknown values.
Given: V1 = 7.5 L P1 = 100 kPa V2 = 11 L
Unknown: P2

11. Math Skills, continued
2. Write the equation for Boyle’s law, and rearrange the equation to solve for P2.
3. Insert the known values into the equation, and solve.
P1V1 = P2V2
P2 = 68 kPa

12. Gas Laws, continued
Gay-Lussac’s law relates gas pressure to temperature.
Gay-Lussac’s law: The pressure of a gas increases as the temperature increases, if the volume of the gas does not change. The pressure decreases as the temperature decreases.
Charles’s law relates temperature to volume.
Charles’s law: For a fixed amount of gas at a constant pressure, the volume of the gas increases as the gas’s temperature increases. Likewise, the volume of the gas decreases as the gas’s temperature decreases.

13. Visual Concept: Charles’s Law