1. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

2. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Gases and Gas Pressure
Gas mixtures are homogeneous and compressible.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

3. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Gases and Gas Pressure
Unit area
Force
Pressure:
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

4. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Gases and Gas Pressure
Barometer
Unit area
Force
Pressure:
Mercury is used in barometers because of its density: 13.6 g/mL.
A corresponding water barometer would be 3 stories high!
The Journal of Chemical Education published an article about constructing one-
de Grys, Hans; Thirty Feet and Rising: Constructing and Using a Water Barometer To Explore Chemical Principles; J. Chem. Educ. 2003, 80, 1156.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

5. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Gases and Gas Pressure
Units
Barometer Pa
torr
mm Hg
atm
bar
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

6. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Gases and Gas Pressure
Units
Conversions Pa
torr
mm Hg
atm
bar
1 atm = 760 mm Hg
(exact)
1 torr = 1 mm Hg
(exact)
1 bar = 1 x 105 Pa
(exact)
1 atm = Pa
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

7. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Copyright © 2008 Pearson Prentice Hall, Inc.

8. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Gas Laws
Ideal Gas: A gas whose behavior follows the gas laws exactly.
The physical properties of a gas can be defined by four variables:
P pressure
T temperature
V volume
n number of moles
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

9. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Gas Laws
Boyle’s Law a V P 1
(constant n and T)
PV = k
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

10. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Gas Laws
Boyle’s Law a V P 1
(constant n and T)
PV = k
PinitialVinitial = PfinalVfinal
One goes up, the other one goes down.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

11. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Gas Laws
Charles’ Law
V a T
(constant n and P)
= k T V
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

12. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Gas Laws
Charles’ Law
V a T
(constant n and P)
= k T V =
Tfinal
Vfinal
Tinitial
Vinitial
One goes up, the other one goes up.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

13. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Gas Laws
Avogadro’s Law
V a n
(constant T and P)
= k n V =
nfinal
Vfinal
ninitial
Vinitial
One goes up, the other one goes up.
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Copyright © 2008 Pearson Prentice Hall, Inc.

14. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Ideal Gas Law
Summary
Boyle’s Law:
PinitialVinitial = PfinalVfinal =
Tfinal
Vfinal
Tinitial
Vinitial
Charles’ Law:
It is not necessary to know the names of the gas laws in order to solve problems. If one remembers the relationships between pressure, volume, temperature, and moles, then one can determine how to work the problem.
ninitial
Vinitial
nfinal
Vfinal
Avogadro’s Law: =
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

15. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Ideal Gas Law
These values are all around 22 L for 1 mol of gas.
Is there a mathematical relationship between
P, V, n, and T for an ideal gas?
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

16. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Ideal Gas Law
Ideal Gas Law:
PV = nRT
R is the gas constant and is the same for all gases.
R =
K mol
L atm
T = 0 °C ( K)
Standard Temperature and Pressure (STP) for Gases
Standard pressure is actually 1 bar.
Gas law problems must use Kelvin!!!!!!
P = 1 atm
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

17. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Ideal Gas Law
What is the volume of 1 mol of gas at STP?
The closer the molar volume of a gas is to L at STP, the more ideal the behavior.
(1 atm)
(1 mol)
K mol
L atm
( K) P
nRT
V = =
= L
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

18. Stoichiometric Relationships with Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Stoichiometric Relationships with Gases
The reaction used in the deployment of automobile airbags is the high-temperature decomposition of sodium azide, NaN3, to produce N2 gas. How many liters of N2 at 1.15 atm and 30.0 °C are produced by decomposition of 45.0 g NaN3?
2Na(s) + 3N2(g)
2NaN3(s)
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Copyright © 2008 Pearson Prentice Hall, Inc.

19. Stoichiometric Relationships with Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Stoichiometric Relationships with Gases
2Na(s) + 3N2(g)
2NaN3(s)
Moles of N2 produced:
45.0 g NaN3
65.0 g NaN3
1 mol NaN3
2 mol NaN3
3 mol N2 x x
= 1.04 mol N2
Volume of N2 produced:
(1.15 atm)
(1.04 mol)
K mol
L atm
( K) P
nRT
V = =
= 22.5 L
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Copyright © 2008 Pearson Prentice Hall, Inc.

20. Partial Pressure and Dalton’s Law
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Partial Pressure and Dalton’s Law
Dalton’s Law of Partial Pressures: The total pressure exerted by a mixture of gases in a container at constant V and T is equal to the sum of the pressures of each individual gas in the container.
Ptotal = P1 + P2 + … + PN
Total moles in mixture
Moles of component
I’ve just presented the result for mole fraction in terms of component and total pressures without showing the derivation.
Mole Fraction (X) =
Xi =
ntotal ni
Xi =
Ptotal Pi or
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Copyright © 2008 Pearson Prentice Hall, Inc.

21. The Kinetic-Molecular Theory of Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Kinetic-Molecular Theory of Gases
A gas consists of tiny particles, either atoms or molecules, moving about at random.
The volume of the particles themselves is negligible compared with the total volume of the gas; most of the volume of a gas is empty space.
The gas particles act independently of one another; there are no attractive or repulsive forces between particles.
Collisions of the gas particles, either with other particles or with the walls of a container, are elastic (constant temperature).
The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the sample.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

22. Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Copyright © 2008 Pearson Prentice Hall, Inc.

23. The Kinetic-Molecular Theory of Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Kinetic-Molecular Theory of Gases
molar
mass
average
speed
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

24. The Kinetic-Molecular Theory of Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Kinetic-Molecular Theory of Gases
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

25. Graham’s Law: Diffusion and Effusion of Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Graham’s Law: Diffusion and Effusion of Gases
Diffusion: The mixing of different gases by molecular motion with frequent molecular collisions.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

26. Graham’s Law: Diffusion and Effusion of Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
Graham’s Law: Diffusion and Effusion of Gases
Effusion: The escape of a gas through a pinhole into a vacuum without molecular collisions. a
Rate 1 m
Graham’s Law:
m is mass.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

27. The Behavior of Real Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Behavior of Real Gases
The volume of a real gas is larger than predicted by the ideal gas law.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

28. The Behavior of Real Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Behavior of Real Gases
Attractive forces between particles become more important at higher pressures.
Particles are closer together at higher pressures due to the increased attractive forces.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

29. The Behavior of Real Gases
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Behavior of Real Gases
van der Waals equation
Correction for intermolecular attractions. a n2 P +
V - n b
= nRT V2
Correction for molecular volume.
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

30. The Earth’s Atmosphere
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Earth’s Atmosphere
Copyright © 2008 Pearson Prentice Hall, Inc.
Copyright © 2008 Pearson Prentice Hall, Inc.

31. The Earth’s Atmosphere
Chapter 9: Gases: Their Properties and Behavior
6/19/2019
The Earth’s Atmosphere
Copyright © 2008 Pearson Prentice Hall, Inc.