1. Properties of Gases

2. Kinetic Theory of Gases
Many independent particles
Random motion at high speed
Separated by great distances

3. Kinetic Theory of Gases
Interact only when they collide
5. Elastic collisions

4. Physical Properties of Gases
Diffusion
Effusion
Permeability
Compressibility
Expansibility

5. spontaneous mixing due to particle motion
Diffusion
spontaneous mixing due to particle motion

6. gas particles passing through a tiny opening into an evacuated area
Effusion
gas particles passing through a tiny opening into an evacuated area

7. Both diffusion and effusion are directly related to the speed of the gas molecules.

8. Graham’s Law of Effusion
rate of effusion for gas 1
molar mass2 =
rate of effusion for gas 2
molar mass1

9. Sample Problem 1
Calculate the ratio of effusion rates between nitrogen (N2) and Argon (Ar).
molar massN = g/mol
molar massAr = g/mol

10. rate of effusion for gas 1 rate of effusion for gas 2
Sample Problem 1
rate of effusion for N2
rate of effusion for gas 1
molar mass2
39.95 g/mol =
rate of effusion for Ar
rate of effusion for gas 2
molar mass1
28.02 g/mol
= 1.194

11. Sample Problem 1
The result indicates that the lighter nitrogen gas will effuse times faster than the argon gas.

12. Permeability
the property of a substance that allows another substance’s particles to spread or flow throughout it

13. Compressibility
the property of a substance that allows its particles to be squeezed into smaller volumes

14. Expansibility
the property of a substance that allows its particles to spread out
Expansibility is caused by pressure differences.

15. Question Why can gases expand so much? Random motion
Elastic collisions
Independent particles
Touching particles
Particles locked together

16. Question Why can gases contract so much?
Separation of particles by great distances
Random motion
Particle interaction only when they collide
Elastic collisions
They cannot contract.

17. average force per unit area
Gas Pressure
average force per unit area

18. What causes
pressure?
collisions

19. What causes
collisions?
motion

20. Question What is the root cause of pressure? Collisions Motion Force
Permeability

21. Units of Pressure 1 atmosphere (atm) = 14.7 lb./in2 (psi) = 760 torr
= 760 mm Hg – a standard unit of pressure used in barometers

22. Units of Pressure pascals (Pa) – the SI unit of pressure
1 atm = 101,325 Pa
= kPa

23. Barometer
an apparatus that measures atmospheric pressure by its support of a column of liquid

24. Earth’s normal atmospheric pressure at sea level is 1 atm.
Atmosphere
Earth’s normal atmospheric pressure at sea level is 1 atm.
(1 atm = 760 mm Hg)

25. Sample Problem 2 17 atm 760 mm Hg = 12,920 mm Hg 1 atm
If a submarine is under a pressure of 17 atm, what is this pressure in mm Hg?
17 atm
760 mm Hg
= 12,920 mm Hg
1 atm

26. Question
If a bird is under a pressure of 800 torr, what is the pressure in atm?
0.94 atm
54.42 atm
608,000 atm
1.05 atm

27. Question
If a bird is under a pressure of 800 torr, what is the pressure in atm?
800 torr
1 atm
= 1.05 atm
760 torr

28. Pressure, Volume, and Temperature
These three conditions of a gas are interrelated.

29. Properties of Gases 0° 500° Relative number of molecules
Chemistry textbook, p. 247
Molecular speed