1. Chapter 6 Gases
6.3
Pressure and Volume
Boyle’s Law

2. Boyle’s Law Boyle’s law states that
the pressure of a gas is inversely related to its volume when T and n are constant
the product P  V is constant when temperature and moles are held constant
if volume decreases, the pressure increases
P1V1 = P2V2

3. Boyle’s Law: PV = Constant
P1V1 = 8.0 atm  2.0 L = 16 atm L
P2V2 = 4.0 atm  4.0 L = 16 atm L
P3V3 = 2.0 atm  8.0 L = 16 atm L
Boyle’s law can be stated as
P1V1 = P2V2 (T, n constant)

4. Boyle’s Law and Breathing
During an inhalation,
the lungs expand
the pressure in the lungs decreases
air flows toward the lower pressure in the lungs

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

6. Solving for a Gas Law Factor
The equation for Boyle’s law can be rearranged to
solve for any factor.
P1V1 = P2V Boyle’s law
To solve for V2 , divide both sides by P2.
P1V1 = P2V2
P P2
V1 x P1 = V2 P2

7. Barometer Measures Pressure
A barometer
measures the pressure exerted by the gases in the atmosphere
indicates atmospheric pressure as the height in mm of the mercury column
760 mmHg = 1 atm

8. Atmospheric Pressure Atmospheric pressure is the pressure exerted by
a column of air from the
top of the atmosphere to
the surface of Earth
decreases as altitude increases
is 1 atm at sea level
is higher on a rainy day

9. Guide to Using Gas Laws

10. Calculations Using Boyle’s Law
Freon-12, CCl2F2, is used in refrigeration systems. What
is the new volume (L) of a 8.0-L sample of Freon gas
initially at 550 mmHg after its pressure is changed to
2200 mmHg at constant T and n?
Step 1 Organize the data in a table of initial and final conditions.
Conditions Initial Final
P1 = mmHg P2 = mmHg
V1 = L V2 = ?

11. Solution Step 2 When pressure increases, volume decreases.
Solve Boyle’s law for V2:
P1V1 = P2V V2 = V1 P1 P2
Step 3 Substitute values into the gas law equation and calculate.
V2 = L  550 mmHg = 2.0 L
2200 mmHg
pressure ratio
decreases volume

12. Learning Check 12
A sample of oxygen gas has a volume of 12.0 L at mmHg. What is the new pressure when the volume changes to 36.0 L (T and n constant)?
A mmHg
B mmHg
C mmHg

13. Solution A sample of oxygen gas has a volume of 12.0 L at13
A sample of oxygen gas has a volume of 12.0 L at
600. mmHg. What is the new pressure when the volume
changes to 36.0 L (T and n constant)?
Step 1 Organize the data in a table of initial and final conditions.
Data Table
Conditions 1 Conditions 2
P1 = mmHg P2 = ?
V1 = L V2 = L

14. Solution A sample of oxygen gas has a volume of 12.0 L at14
A sample of oxygen gas has a volume of 12.0 L at
600. mmHg. What is the new pressure when the volume
changes to 36.0 L (T and n constant)?
Step 2 Rearrange the gas law equation to solve for the unknown quantity.
P2 = P1  V1 V2
Step mmHg  12.0 L = mmHg The answer is A L
The answer is A, 200. mmHg.

15. Learning Check 15
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).
1. pressure decreases
2. pressure increases

16. Learning Check 16
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).
1. pressure decreases cylinder B
2. pressure increases cylinder A

17. Learning Check If a sample of helium gas has a volume of 120 mL and a17
If a sample of helium gas has a volume of 120 mL and a
pressure of 850 mmHg, what is the new volume if the
pressure is changed to 425 mmHg?
A. 60 mL B mL C mL

18. Solution If a sample of helium gas has a volume of 120 mL and a18
If a sample of helium gas has a volume of 120 mL and a
pressure of 850 mmHg, what is the new volume if the
pressure is changed to 425 mmHg?
Step 1 Organize the data in a table of initial and final conditions.
Data Table
Conditions Conditions 2
P1 = mmHg P2 = mm Hg
V1 = mL V2 = ?
Step 2 Rearrange the gas law equation to solve for the unknown quantity. V2 = V1  P1 P2

19. Solution If a sample of helium gas has a volume of 120 mL and a19
If a sample of helium gas has a volume of 120 mL and a
pressure of 850 mmHg, what is the new volume if the
pressure is changed to 425 mmHg?
Step 3 Substitute values into the gas law equation and calculate.
V2 = V1  P1 = mL  850 mmHg = 240 mL
P mmHg Pressure ratio
increases volume
The answer is C, 240 mL.

20. Learning Check 20
A sample of helium gas in a balloon has a volume of 6.4 L at a pressure of 0.70 atm. At 1.40 atm (T is constant), is the new volume represented by A, B, or C?

21. Solution 21
A sample of helium gas in a balloon has a volume of 6.4 L at a pressure of 0.70 atm. At a higher pressure (T constant), the new volume is represented by the smaller balloon A.