1. General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 7
Gases
7.3
Pressure and Volume
(Boyle’s Law)
Lectures
© 2013 Pearson Education, Inc.

2. Boyle’s Law Boyle’s law states that
the pressure of a gas is inversely related to its volume when temperature (T) and amount of gas (n) are constant.
if the pressure (P) increases, then the volume (V) decreases. 2

3. PV Constant in Boyle’s Law
the product P × V is constant as long as T and n do not change.
it can be stated that since P × V is a constant. P1V1 = P2V2 (T, n constant) 3

4. Guide to Using Gas Laws 4

5. Solving for a Gas Law Factor
A sample of nitrogen gas (N2) has a volume of 4.2 L at 1.0 atm. If the pressure is decreased to 0.75 atm with no change in the temperature or amount of gas, what will be the new volume?
Step 1 Organize the data in a table of initial and
final conditions.
Analyze the Problem.
Factors T and n remain constant.
Conditions 1
Conditions 2
Know
Predict
V1 = 4.2 L
V2 = ?
V increases
P1 = 1.0 atm
P2 = 0.75 atm
P decreases 5

6. Solving for a Gas Law Factor
A sample of nitrogen gas (N2) has a volume of 4.2 L
at 1.0 atm. If the pressure is decreased to 0.75 atm
with no change in the temperature or amount of
gas, what will be the new volume?
Step 2 Rearrange the gas law equation to solve for the unknown quantity.
P1V1 = P2V Boyle’s Law
To solve for V2 , divide both sides by P2. 6

7. Solving for a Gas Law Factor
A sample of nitrogen gas (N2) has a volume of 4.2 L
at 1.0 atm. If the pressure is decreased to 0.75 atm
with no change in the temperature or amount of
gas, what will be the new volume?
Step 3 Substitute values into the gas law equation and calculate. 7

8. Boyle’s Law and Breathing: Inhalation
During inhalation,
the lungs expand,
the pressure in the lungs decreases, and
air flows towards the lower pressure in the lungs. 8

9. Boyle’s Law and Breathing: Exhalation
During exhalation,
lung volume decreases,
pressure within the lungs increases, and
air flows from the higher pressure in the lungs to the outside. 9

10. Learning Check
Freon-12 gas, a fluorocarbon, CCl2F2, is used in refrigeration systems. What is the new volume (L) of an 8.0 L sample of Freon after its pressure is changed from 550 mmHg to 2200 mmHg at constant T? 10

11. Solution
What is the new volume (L) of an 8.0 L sample of Freon after its pressure is changed from 550 mmHg to
2200 mmHg at constant T?
Step 1 Organize the data in a table of initial and final conditions.
Analyze the Problem.
Conditions 1
Conditions 2
Know
Predict
P1 = 550 mmHg
P2 = 2200 mmHg
P increases
V1 = 8.0 L
V2 = ?
V decreases 11

12. Solution What is the new volume (L) of an 8.0 L sample of Freon
after its pressure is changed from 550 mmHg to
2200 mmHg at constant T?
Step 2 Rearrange the gas law equation to solve for the unknown quantity.
P1V1 = P2V2 12

13. Solution What is the new volume (L) of an 8.0 L sample of Freon
after its pressure is changed from 550 mmHg to
2200 mmHg at constant T?
Step 3 Substitute values into the gas law equation and calculate.
pressure ratio
decreases volume 13

14. Learning Check
For a cylinder containing helium gas, indicate if cylinder A or cylinder B represents the new volume for the following changes (n and T are constant).
A. Pressure decreases.
B. Pressure increases. 14

15. Solution
For a cylinder containing helium gas, indicate if cylinder A or cylinder B represents the new volume for the following changes (n and T are constant).
A. Pressure decreases (cylinder B).
B. Pressure increases (cylinder A). 15