1. Basic Chemistry Chapter 11 Gases Chapter 11 Lecture
Fourth Edition
Chapter Gases
11.3 Pressure and Volume (Boyle’s Law)
Learning Goal Use the pressure-volume relationship (Boyle’s law) to determine the final pressure or volume when the temperature and amount of gas are constant.

2. Boyle’s law states that
the pressure (P) of a gas is inversely related to its volume (V) when T and n are constant
if the pressure (P) increases, then the volume (V) decreases
Figure 11.4 Boyle’s law: As
Volume decreases, gas molecules become more crowded, which causes the pressure to increase. Pressure and volume are inversely related.

3. Boyle’s Law
Boyle’s law is an indirect relationship between pressure and volume. An indirect relationship between variables means as one variable increases the second decreases.
P1V1 = P2V2 Temperature and moles are constant.

4. Boyle’s Law Equation
The equation for Boyle’s law can be rearranged to solve for any factor. At a constant temperature and amount of gas:
P1V1 = P2V Boyle’s law
To obtain V2, divide both sides by P2.

5. Guide to Using the Gas Laws

6. Learning Check
Freon-12, CCl2F2, is a gas used in refrigeration systems. What is the new volume (L) of an 8.0-L sample of Freon gas initially at 550 mmHg after its pressure is changed to 2200 mmHg at constant T?

7. Solution
What is the new volume (L) of an 8.0-L sample at 550 mmHg after its pressure is changed to 2200 mmHg at constant T?
Step 1 Organize the data in a table of initial and final conditions. We can predict that as P increases, V decreases.
Conditions 1
Conditions 2
P1 = mmHg
P2 = mmHg
V1 = L
V2 = ?

8. Solution
What is the new volume (L) of an 8.0-L sample at 550 mmHg after its pressure is changed to 2200 mmHg at constant T?
Step 2 Rearrange the gas law equation to solve for the unknown quantity.
Solve Boyle’s law for V2. Increasing P decreases V when n and T are constant.

9. Solution
What is the new volume (L) of an 8.0-L sample at 550 mmHg after its pressure is changed to 2200 mmHg at constant T?
Step 3 Substitute values into the gas law equation and calculate.
The pressure ratio decreases the volume.

10. Learning Check
For a cylinder containing helium gas, indicate if cylinder A or B represents the new volume for the following changes (n and T are constant):
Pressure decreases
Pressure increases

11. Solution
For a cylinder containing helium gas, indicate if cylinder A or B represents the new volume for the following changes (n and T are constant):
Pressure decreases Cylinder B
Pressure increases Cylinder A

12. Learning Check
A balloon of helium gas has a volume of 6.4 L at a pressure of atm. At 1.40 atm (T and n constant), is the new volume represented by A, B, or C?

13. Solution
A balloon of helium gas has a volume of 6.4 L at a pressure of atm. At 1.40 atm (T and n constant), is the new volume represented by A, B, or C?
At a higher pressure (T and n constant), the new volume is represented by the smaller balloon A.

14. Chemistry Link to Health
During inhalation,
the lungs expand
the pressure in the lungs decreases
air flows toward the lower pressure in the lungs

15. Chemistry Link to Health
During exhalation,
lung volume decreases
pressure within the lungs increases
air flows from the higher pressure in the lungs to the outside