1. Pressure and Volume (Boyle’s Law)
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.
if volume decreases, the pressure increases.

3. PV Constant in Boyle’s Law
In Boyle’s Law, the product P x V is constant as long as T and n do not change.
P1V1 = atm x L = atm L
P2V2 = atm x L = atm L
P3V3 = atm x L = atm L
Boyle’s Law can be stated as
P1V1 = P2V2 (T, n constant)

4. 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

5. Boyles’ Law and Breathing
During an inhalation,
the lungs expand.
the pressure in the lungs decreases.
air flows towards the lower pressure in the lungs.
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Publishing as Benjamin Cummings

6. Boyles’ 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.
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

7. Calculations with Boyle’s Law

8. Calculation with 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 mm Hg after its pressure is changed to 2200 mm Hg at constant T?
1. Set up a data table:
Conditions 1 Conditions 2
P1 = mm Hg P = mm Hg
V1 = L V2 = ?

9. Calculation with Boyle’s Law (Continued)
2. When pressure increases, volume decreases.
Solve Boyle’s Law for V2:
P1V1 = P2V2
V = V1 x P1 P2
V = L x 550 mm Hg = L
2200 mm Hg
pressure ratio
decreases volume

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

11. Solution 1) Pressure decreases B 2) Pressure increases A
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 B
2) Pressure increases A

12. Learning Check If a sample of helium gas has a volume of 120 mL
and a pressure of 850 mm Hg, what is the new
volume if the pressure is changed to 425 mm Hg ?
1) 60 mL ) 120 mL 3) 240 mL

13. Solution P1 = 850 mm Hg P2 = 425 mm Hg V1 = 120 mL V2 = ??
V2 = V1 x P1 = mL x mm Hg = 240 mL
P mm Hg Pressure ratio
increases volume

14. Learning Check
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 constant), is the new volume represented by A, B, or C?

15. Solution
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.

16. Learning Check A) 3.2 L B) 6.4 L C) 12.8 L
If the sample of helium gas has a volume of 6.4 L at a pressure of 0.70 atm, what is the new volume when the pressure is increased to 1.40 atm (T constant)?
A) 3.2 L B) 6.4 L C) 12.8 L

17. Solution
If the sample of helium gas has a volume of 6.4 L at a pressure of atm, what is the new volume when the pressure is increased to 1.40 atm (T constant)?
A) 3.2 L
V2 = V1 x P1 P2
V2 = 6.4 L x atm = L
1.40 atm
Volume decreases when there is an increase in the pressure (temperature is constant.)

18. Learning Check 1) 200. mm Hg 2) 400. mm Hg 3) 1200 mm Hg
A sample of oxygen gas has a volume of 12.0 L at 600. mm Hg. What is the new pressure when the volume changes to 36.0 L? (T and n constant).
1) mm Hg
2) mm Hg
3) 1200 mm Hg

19. Solution 1) 200. mm Hg Data table Conditions 1 Conditions 2
P1 = mm Hg P2 = ???
V1 = L V2 = L
P2 = P1 x V1 V2
600. mm Hg x L = mm Hg L