1. Chapter 7 Gases Pressure and Volume (Boyle’s Law)
Temperature and Volume
(Charles’ Law)
Temperature and Pressure
(Gay-Lussac’s Law)

2. Pressure and Volume P1V1= 8.0 atm x 2.0 L = 16 atm L
Experiment Pressure Volume P x V
(atm) (L) (atm x L)
_____
_____
_____
Boyle's Law P x V = k (constant) when
T remains constant
P1V1= atm x L = atm L
P2V2= atm x L = atm L
P1V1 = P2V2 = k
Use this equation to calculate how a volume changes when pressure changes, or how pressure changes when volume changes.
new vol. old vol. x Pfactor new P old P x Vfactor
V = V x P P2 = P1 x V1
P V2

3. P and V Changes P1 P2 V1 V2

4. Boyle's Law
The pressure of a gas is inversely related to the volume when T does not change
Then the PV product remains constant
P1V1 = P2V2
P1V1= atm x L = atm L
P2V2= atm x L = atm L

5. PV Problem
Freon-12, CCl2F2, is used in refrigeration systems. What is the new volume (L) of a 1.6 L sample of Freon gas initially at 50 mm Hg after its pressure is changed to 200 mm Hg at constant T?

6. PV Calculation DATA TABLE Initial conditions Final conditions
Prepare a data table
DATA TABLE
Initial conditions Final conditions
P1 = 50 mm Hg P2 = 200 mm Hg
V1 = L V2 = ? ?

7. Find New Volume (V2) Solve for V2: P1V2 = P2V2 V2 = V1 x P1 /P2
V2 = L x 50 mm Hg = L
200 mm Hg

8. Learning Check GL1
A sample of nitrogen gas is 6.4 L at a pressure of atm. What will the new volume be if the pressure is changed to 1.40 atm? (T constant) Explain.
1) 3.2 L
2) 6.4 L
3) 12.8 L

9. Solution GL1
A sample of nitrogen gas is 6.4 L at a pressure of atm. What will the new volume be if the pressure is changed to 1.40 atm? (T constant)
6.4 L x atm = L (1)
1.40 atm
Volume must decrease to cause an increase in the pressure

10. Learning Check GL2
A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? (T constant) Explain.
1) mmHg
2) mmHg
3) 1200 mmHg

11. Solution GL2
A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? (T constant) Explain.
600. mm Hg x L = mmHg (1)
36.0 L
Pressure decrease when volume increases.

12. Charles’ Law V = 125 mL V = 250 mL T = 273 K T = 546 K
Observe the V and T of the balloons. How does volume change with temperature?

13. Charles’ Law: V and T At constant pressure, the volume of a gas is
directly related to its absolute (K) temperature
V1 = V2
T T2

14. Learning Check GL3 Use Charles’ Law to complete the statements below:
1. If final T is higher than initial T, final V
is (greater, or less) than the initial V.
2. If final V is less than initial V, final T is
(higher, or lower) than the initial T.

15. Solution GL3
V1 = V2
T T2
1. If final T is higher than initial T, final V
is (greater) than the initial V.
2. If final V is less than initial V, final T is (lower) than the initial T.

16. V and T Problem
A balloon has a volume of 785 mL on a Fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon?

17. VT Calculation Complete the following setup:
Initial conditions Final conditions
V1 = 785 mL V2 = ?
T1 = 21°C = 294 K T2 = 0°C = 273 K
V2 = _______ mL x __ K = _______ mL
V K
Check your answer: If temperature decreases,
V should decrease.

18. Learning Check GL4
A sample of oxygen gas has a volume of 420 mL at a temperature of 18°C. What temperature (in °C) is needed to change the volume to 640 mL?
1) 443°C 2) 170°C ) °C

19. Solution GL4
A sample of oxygen gas has a volume of 420 mL at a temperature of 18°C. What temperature (in °C) is needed to change the volume to 640 mL?
2) 170°C
T2 = K x 640 mL = K
420 mL
= 443 K K = 170°C

20. Gay-Lussac’s Law: P and T
The pressure exerted by a confined gas is directly related to the temperature (Kelvin) at constant volume.
P (mm Hg) T (°C)

21. Learning Check GL5
Use Gay-Lussac’s law to complete the statements below:
1. When temperature decreases, the
pressure of a gas (decreases or increases).
2. When temperature increases, the pressure
of a gas (decreases or increases).

22. Solution GL5 1. When temperature decreases, the
pressure of a gas (decreases).
2. When temperature increases, the
pressure of a gas (increases).

23. PT Problem
A gas has a pressure at 2.0 atm at 18°C. What will be the new pressure if the temperature rises to 62°C? (V constant)
T = 18°C T = 62°C

24. PT Calculation P1 = 2.0 atm T1 = 18°C + 273 = 291 K
P2 = ? T2 = 62°C = 335 K
What happens to P when T increases?
P increases (directly related to T)
P2 = P1 x T2 T1
P2 = atm x K = atm K ?

25. Learning Check GL6 Complete with 1) Increases 2) Decreases
3) Does not change
A. Pressure _____, when V decreases
B. When T decreases, V _____.
C. Pressure _____ when V changes from 12.0 L to 24.0 L (constant n and T)
D. Volume _____when T changes from 15.0 °C to 45.0°C (constant P and n)

26. Solution GL6 A. Pressure 1) Increases, when V decreases
B. When T decreases, V 2) Decreases
C. Pressure 2) Decreases when V changes
from 12.0 L to 24.0 L (constant n and T)
D. Volume 1) Increases when T changes from 15.0 °C to 45.0°C (constant P and n)