1. Chapter 9: Gases: Their Properties and Behavior
4/23/2017
Copyright © 2008 Pearson Prentice Hall, Inc.

2. Stoichiometric Relationships with Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
Stoichiometric Relationships with Gases
Methanol (CH3OH) can be synthesized by the following reaction:
CO(g) H2(g)  CH3OH(g)
What volume (in Liters) of hydrogen gas, measured at a temperature of 355K and a pressure of 738 mmHg, is required to synthesize 35.7 g of methanol?
Copyright © 2008 Pearson Prentice Hall, Inc.

3. Examples Consider the reaction represented by the equation
P4(s) H2(g)  4H3(g)
What is the amount of P4 is required to react with 5.39 L of hydrogen gas at 27.0oC and 1.25 atm?

4. Partial Pressure and Dalton’s Law
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
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
Mole Fraction (X) =
I’ve just presented the result for mole fraction in terms of component and total pressures without showing the derivation.
Xi =
ntotal ni
Xi =
Ptotal Pi or
Copyright © 2008 Pearson Prentice Hall, Inc.

5. Examples
Determine the mole fractions and partial pressures of CO2, CH4, and He in a sample of gas that contains mole of CO2, 1.29 moles of CH4, and 3.51 moles of He, and in which the total pressure is 5.78 atm

6. Example
A 1.00 L vessels contain mole of N2 gas and mole of H2 gas at 25.5oC. Determine the partial pressure of each component and the total pressure

7. The Kinetic-Molecular Theory of Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
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.
Copyright © 2008 Pearson Prentice Hall, Inc.

8. The Kinetic-Molecular Theory of Gases
3. Collisions of the gas particles, either with other particles or with the walls of a container, are elastic (constant temperature).
4. The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the sample.

9. Chapter 9: Gases: Their Properties and Behavior
4/23/2017
Copyright © 2008 Pearson Prentice Hall, Inc.

10. The Kinetic-Molecular Theory of Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
The Kinetic-Molecular Theory of Gases
molar
mass
average
speed
Copyright © 2008 Pearson Prentice Hall, Inc.

11. The Kinetic-Molecular Theory of Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
The Kinetic-Molecular Theory of Gases
Copyright © 2008 Pearson Prentice Hall, Inc.

12. Graham’s Law: Diffusion and Effusion of Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
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.

13. Graham’s Law: Diffusion and Effusion of Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
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.

14. Graham’s Law: Diffusion and Effusion of Gases
In comparing two gases at the same temperature and pressure
√m2
√m1
Rate 1 =
Rate 2

15. Example
Determine how much faster Helium atoms moves, on average, than a carbon dioxide molecule at the same temperature
Determine the molar mass and identity of a gas that moves 4.67 times as fast as CO2

16. The Behavior of Real Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
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.

17. The Behavior of Real Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
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.

18. The Behavior of Real Gases
Chapter 9: Gases: Their Properties and Behavior
4/23/2017
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.

19. Example
A sample of 3.50 moles of NH3 gas occupies 5.20 L at 47oC. Calculate the pressure of the gas (in atm) using
A) the ideal gas equation
B) the van der Waals equation
a = 4.17 atm •L/mol2 b = L/mol