1. Gases
Properties of Gases
Gas Pressure

2. Gases
What gases are important for each of the following: O2, CO2 and/or He?
A B C D.

3. Gases
What gases are important for each of the following: O2, CO2 and/or He?
A. CO B. O2/CO C. O2 D. He

4. Some Gases in Our Lives Air: oxygen O2 nitrogen N2 ozone O3
argon Ar carbon dioxide CO2 water H2O
Noble gases:
helium He neon Ne krypton Kr xenon Xe
Other gases:
fluorine F2 chlorine Cl2 ammonia NH3
methane CH4 carbon monoxide CO
nitrogen dioxide NO2 sulfur dioxide SO2

5. The Nature of Gases Gases are compressible
Why can you put more air in a tire, but can’t add more water to a glass full of water?
Gases have low densities
Dsolid or liquid = 2 g/mL
Dgas 2 g/L

6. Nature of Gases 1. Why does a round balloon
become spherical when filled
with air?
2. Suppose we filled this room halfway with water. Where would pressure be exerted?

7. Nature of Gases Gases fill a container completely and uniformly
Gases exert a uniform pressure on all inner surfaces of their containers

8. Kinetic Theory of Gases
The particles in gases
Are very far apart
Move very fast in straight lines until they collide
Have no attraction (or repulsion)
Move faster at higher temperatures

9. Barometers
760 mmHg
atm
pressure

10. Learning Check G1
A.The downward pressure of the Hg in a barometer is _____ than (as) the weight of the atmosphere.
1) greater 2) less 3) the same
B.A water barometer has to be 13.6 times taller than Hg barometer (DHg = 13.6 g/mL)
because
1) H2O is less dense 2) Hg is heavier
3) air is more dense than H2O

11. Solution G1
A.The downward pressure of the Hg in a barometer is 3) the same (as) the weight of the atmosphere.
B.A water barometer has to be 13.6 times taller than Hg barometer (DHg = 13.6 g/mL)
because
1) H2O is less dense

12. Unit of Pressure
One atmosphere (1 atm)
Is the average pressure of the atmosphere at sea level
Is the standard of pressure
P = Force
Area
1.00 atm = 760 mm Hg = 760 torr

13. Learning Check G2 1) the weight of the atmosphere pushes it
When you drink through a straw you reduce the pressure in the straw. Why does the liquid go up the straw?
1) the weight of the atmosphere pushes it
2) the liquid is at a lower level
3) there is empty space in the straw
Could you drink a soda this way on the moon?
1) yes ) no 3) maybe
Why or why not?

14. Solution G2 1) the weight of the atmosphere pushes it
When you drink through a straw you reduce the pressure in the straw. Why does the liquid go up the straw?
1) the weight of the atmosphere pushes it
3) there is empty space in the straw
Could you drink a soda this way on the moon?
2) no
Why or why not? Low atmospheric pressure

15. Types of Pressure Units
Pressure Used in
760 mm Hg or 760 torr Chemistry
14.7 lb/in.2 U.S. pressure gauges
29.9 in. Hg U.S. weather reports
101.3 kPa (kilopascals) Weather in all countries except U.S.
1.013 bars Physics and astronomy

16. Learning Check G3 A. What is 475 mm Hg expressed in atm?
1) 475 atm ) atm 3) x 105 atm
B. The pressure of a tire is measured as 29.4 psi.
What is this pressure in mm Hg?
1) mm Hg
2) mm Hg
3) 22,300 mm Hg

17. Solution G3 A. What is 475 mm Hg expressed in atm?
485 mm Hg x atm = atm (B)
760 mm Hg
B. The pressure of a tire is measured as 29.4 psi.
What is this pressure in mm Hg?
29.4 psi x 1.00 atm x 760 mmHg = 1.52 x 103 mmHg
14.7 psi atm (B)

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

19. 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

20. P and V Changes P1 P2 V1 V2

21. 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

22. 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?

23. 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 = ? ?

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

25. 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

26. 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

27. 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

28. 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.

29. 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?

30. 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

31. 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.

32. 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.

33. 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?

34. 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.

35. 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

36. 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

37. 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)

38. 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).

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

40. 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

41. 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 ?

42. 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)

43. 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)