1. Chapter 12
Properties Of Gases

2. Pressure
Measure of the number of collisions between gas particles and a unit area of the wall of the container Pressure = force / unit area

3. Force/area English system: pounds/in2 (psi) Metric system:
Newton/m2 (pascal)

4. Torricelli Barometer
h = 760 mm Hg
1 atmosphere
pressure

5. 1 atm = 760 torr (mm Hg)
= kPa
= bar
=14.70 psi

7. Patm
Manometer h
Pgas

8. Patm
Manometer h
Pgas

9. Volume
Total space of a container that gases occupy due to the free random motion of the gas molecules

10. Relationship between Volume & Pressure of Gases
P-V

11. V
P (at constant T)

12. Slope = k V
1/P (at constant T)

13. In mathematical terms:
y = mx + b
Boyle’s Law

14. Relationship between Volume & Temperature of Gases
V-T

15. In mathematical terms:
y = mx + b
V = mT + b
Charles’ Law

16. Where T must be in Kelvin (K) temperature
K = 0C + 273

18. Relationship between Pressure & Temperature of Gases
P-T

19. In mathematical terms:
y = mx + b
P = mT + b
Gay-Lussac’s Law

20. Relationship between Volume & Moles
of Gases
V-n

21. In mathematical terms:
y = mx + b
V = mn + b
Avogadro’s Law

22. Avogadro’s Hypothesis
At constant temperature and pressure, equal volumes of gases contain equal number of particles

23. Combined Gas Law

24. Ideal & Real
Gasses

25. Kinetic Molecular Theory
1. Gases consist of small particles that are far apart in comparison to their own size. These particles are considered to be tiny points occupying a negligible volume compared to that of their container.

26. Kinetic Molecular Theory
2. Molecules are in rapid and random straight-line motion. This motion can be described by well-defined and established laws of motion.

27. Kinetic Molecular Theory
3. The collisions of molecules with the walls of a container or with other molecules are perfectly elastic. That is, no loss of energy occurs.

28. Kinetic Molecular Theory
4. There are no attractive forces between molecules or between molecules and the walls with which they collide.

29. Kinetic Molecular Theory
5. At any particular instant, the molecules in a given sample of gas do not all possess the same amount of energy.

30. Ideal Gas Equation

32. Note that
is similar to the
Combined Gas Law
derived earlier.

33. Variations on
Ideal Gas Equation

34. Variations on Ideal Gas Equation
Bromine
Variations on
Ideal Gas Equation

35. Real Gas
Behavior

36. Ideal Gas
Equation
P V = n R T

37. N2
2.0
CH4 H2 PV
nRT
1.0
Ideal
gas
CO2
P (atm)

38. “correct” for volume of molecules
(V - b)

39. attractive forces between molecules
also “correct” for
attractive forces between molecules

40. van der Waals’ Equation
for 1 mole

41. van der Waals’ Equation
for n moles

42. from CRC Handbook
a* b* He Ne
*when P(atm) & V(L)

43. from CRC Handbook
a* b* NH
H2O
*when P(atm) & V(L)

44. from CRC Handbook
a* b*
CCl
C5H
*when P(atm) & V(L)

45. Cl2 gas has a = 6.49, b =
For 8.0 mol Cl2 in a 4.0 L tank at 27oC.
P (ideal) = nRT/V = 49.3 atm
P (van der Waals) = 29.5 atm

46. T & P conditions
where a real gas
approximates
an ideal gas?

47. N2 gas PV nRT 203 K 293 K 1.8 1.4 673 K Ideal 1.0 gas 0.6
P (atm)

48. T & P conditions
where a real gas
approximates
an ideal gas?
high temperature
low pressure

49. Gaseous
Molecular
Movement

50. pressure exerted by each component in a mixture of gases
Partial Pressure
pressure exerted by each component in a mixture of gases

51. this assumes that
NO interactions
occurs between
the molecules of gas

52. must conclude 1. each gas acts as if it is in container alone
2. each gas collides with the container wall as an “event”

53. where n = # components
Or Dalton’s Law
PT = P1 + P2 + P

54. Pi V = ni R T or

55. thus:

56. or

57. therefore:
nT =  ni
and PT  sum of mols
of gas

58. Mole Fraction

60. Since:
and

61. Then

62. and
Pi = Xi PT

64. diffusion is the gradual mixing of molecules of different gases.
effusion is the movement of molecules through a small hole into an empty container.

65. rate of  average
effusion speed

67. But ...
where

68. thus
then
RMS speed

71. substituting:

72. simplifying
Graham’s Law
NH3-HCl

74. if “d” is constant

75. if “t” is constant

76. GAS LAW
STOICHIOMETRY