1. Physical Characteristics of Gases
Chapter 10

2. The Kinetic-Molecular
Section 1:
The Kinetic-Molecular
Theory of Matter

3. Section 1: Kinetic-Molecular Theory of Matter
Kinetic-molecular theory is based on…
All matter is made of particles that are in constant motion.
Is used to explain properties of solids, liquids, & gases.

4. Section 1: Kinetic-Molecular Theory of Matter
Solids, liquids, and gases vary due to the energy of the particles and the forces that act upon them.
This chapter will study gases.

5. Section 1: Kinetic-Molecular Theory of Matter
Theory pertains to ideal gases - not real gases.
An ideal gas is an imaginary gas that perfectly fits all the assumptions of the k-m theory.

6. Section 1: Kinetic-Molecular Theory of Matter
5 assumptions:
1.Gases consist of large numbers of tiny particles that are far apart relative to their size
Much farther apart than liquids & solids so they can be compressed.

7. Section 1: Kinetic-Molecular Theory of Matter
5 assumptions (continued):
2.Collisions are elastic - there is no net loss of kinetic energy. Kinetic energy is completely transferred during collisions.

8. Section 1: Kinetic-Molecular Theory of Matter
5 assumptions (continued):
Kinetic energy is constant (if at same temperature)

9. Section 1: Kinetic-Molecular Theory of Matter
5 assumptions (continued):
3.Gas particles are in constant, rapid, random motion. They have kinetic energy.

10. Section 1: Kinetic-Molecular Theory of Matter
5 assumptions (continued):
4. No forces of attraction act on gas particles.

11. Section 1: Kinetic-Molecular Theory of Matter
5 assumptions (continued):
The average kinetic energy of gas particles depends on the temperature of the gas.
KE= mv2 2

12. Section 1: Kinetic-Molecular Theory of Matter
Consider: KE= mv2 2
What does KE depend on if gases are the same kind?
What does KE depend on if gases are at same temperature but are different kinds of gases?

13. Physical Properties of Gases
Expansion – Completely fill container & take its shape

15. Physical Properties of Gases
Fluidity – Gases have the ability to flow. Particles can glide past each other.

16. Physical Properties of Gases
Low density: Gas densities are about 1/1000 that of the liquid or solid phase.
Compressibility: Steel canisters contain about 100 times the number of particles than at normal pressure.

17. Physical Properties of Gases
Diffusion: Gases randomly move and mix by random motion of their particles.
The rate of diffusion depends on the mass of the particles. Heavier ones move more slowly.

18. Animation of diffusion

19. Physical Properties of Gases
Effusion: Gases under pressure spread out when released from a small opening.

20. Deviations of Real Gases
Real gases do not behave according to all the assumptions of the K-M theory.
Real gases deviate most when they are under very high pressures and very cold temperatures.

21. Reason behind this…
Both high pressure and colder temperatures force the atoms or molecules of a gas closer together.
When real gases get closer together they experience intermolecular attractions and then they condense to form liquids.

22. Deviations of Real Gases
Noble gases behave more like ideal gases than any others.
More polar gases behave less like ideal gases.

23. Section 2:
Pressure

24. To describe a gas you must state 4 quantities: Volume Temperature
Section 2: Pressure
To describe a gas you must state 4 quantities:
Volume
Temperature
Number of molecules
Pressure

25. Pressure is defined as the amount of force per unit of area.
Section 2: Pressure
Pressure is defined as the amount of force per unit of area.
P = force
area

26. Area unit is square meters Pressure = N/m2
Section 2: Pressure
P = force
area
Force unit is Newtons
Area unit is square meters
Pressure = N/m2

27. Section 2: Pressure
Open can
Closed Can
Air Pumped
Out

28. Measuring Pressure
What tool do we use to measure atmospheric pressure?
Barometer!
First built by Evangelista Torricelli (1600’s)

29. Measuring Pressure
Torricelli noticed that pumps could raise water only 34 feet high.
He compared density of mercury to density of water (14x greater)
Predicted height that mercury could be raised (1/14 of 34 ft or about 30 inches).

30. Units of Pressure Several different units are used for pressure:
inches of mercury (ex and rising)
mm of Hg
atm (atmospheres)
torrs
Kilopascals (1 Kpa= 1N/m2)

31. Units of Pressure Standard pressure taken at sea level:
29.9 inches of mercury
760 mm of Hg
1 atm (atmospheres)
760 torrs
101.3 Kilopascals

32. Section 3
The Gas Laws
Mathematical relationships between volume, temperature, pressure and quantity of gases

33. Section 3: The Gas Laws Boyle’s Law Charles’ Law
Dalton’s Law of Partial Pressures
Gay-Lussac’s Law
Combined Gas Law

34. P ↑ V ↓ Section 3: The Gas Laws Boyle’s Law
Relates gas volume to pressure
Has an inverse relationship
P ↑ V ↓

35. P1V1 = P2V2 Section 3: The Gas Laws Formula for Boyle’s Law
What would be a gas’s volume if the pressure reduced from 98 kPa down to 60 kPa if its original volume was 300 Liters?

36. Simulation of Boyle's Law

37. Section 3: The Gas Laws
P1V1 = P2V2
98 (300) = 60 (V2)
V2 = 490 L

38. Relates temperature to gas volume. Directly proportional.
Section 3: The Gas Laws
Charles’ Law
Relates temperature to gas volume.
Directly proportional.
Is based on absolute zero.

39. Section 3: The Gas Laws
In 1787, Jacques Charles found that as he decreased the temperature of a gas 1 degree then the volume decreased 1/273.

40. Section 3: The Gas Laws
The volume of a fixed mass of gas at constant pressure varies directly with the Kelvin temperature.

41. Formula for Charles’ Law (temperature must be in Kelvin)
Section 3: The Gas Laws
Formula for Charles’ Law (temperature must be in Kelvin)
V1 V2 =
T T2

42. Charles’ Law Graph V T

43. Problem:
If the temperature of a gas increases from 25 degrees Celsius up to 80 degree Celsius and the original volume was 10 liters of gas, then what would the final volume be????
10 X
( ) ( )
X = 11.8 liters

44. Gay-Lussac’s Law
P1 P2 =
T T2
Relates pressure and temperature (assumes constant volume)

45. Combined Gas Law
This law is used when 2 variables change – pressure, temperature, or volume.
P1V1 = P2V2
T T2

46. Dalton’s Law of Partial Pressure
If there is no chemical reaction occurring then the pressure of a mixture of gases will be equal to all the combined pressures of each gas.
Equation:
PT = P1 + P2 + P3 + …

47. Collecting Gases by Water Displacement
Water is commonly collected by bubbling it through water.
The pressure then in the container is a combination of both the pressure of the gas as well as a small amount of water vapor.

48. Gas Collection

49. Collecting Gases by Water Displacement
To determine the pressure of the gas you must subtract the pressure of the water vapor.
The pressure of the water varies according to the temperature.
Use the chart for H2O pressure:

50. Vapor Pressure of Water
Temp. (0C)
Vapor Pressure (torr)
Temp (0C) 18
15.5 24
22.4 19
16.5 25
23.8 20
17.5 26
25.2 21
18.6 27
26.7 22
19.8 28
28.3 23
21.2 29
30.3

51. Sample Problem:
Oxygen was collected under water at 20°C. If the combined pressure was 731 torr, then what is the pressure of the gas within?
H2O pressure at 20 C = 17.5 torr
Total press: 731
Minus H2O
Gas press: torr

52. Assignment
Page 329:
questions 39-43