1. 1 Chapter 5: GASES Part 2

2. 2 Dalton’s Law of Partial Pressures  Since gas molecules are so far apart, we can assume that they behave independently.  Dalton’s Law: in a gas mixture, the total pressure is the sum of the partial pressures of each component: P Total = P 1 + P 2 + P 3 +...

3. 3 Using Dalton’s Law: Collecting Gases over Water  Commonly we synthesize gas and collect it by displacing water, i.e. bubbling gas into an inverted container

4. 4 Using Dalton’s Law: Collecting Gases over Water  To calculate the amount of gas produced, we need to correct for the partial pressure of water: P total = P gas + P water

5. 5 Using Dalton’s Law: Collecting Gases over Water Example 3: Mixtures of helium and oxygen are used in scuba diving tanks to help prevent “the bends”. For a particular dive, 46 L of He at 25°C and 1.0 atm and 12 L of O 2 at 25°C and 1.0 atm were each pumped into a tank with a volume of 5.0 L. Calculate the partial pressure of each gas and the total pressure in the tank at 25°C

6. 6 Kinetic Molecular Theory 1.Gases consist of a large number of molecules in constant motion. 2.Volume of individual particles is  zero. 3.Collisions of particles with container walls cause pressure exerted by gas. 4.Particles exert no forces on each other. 5.Average kinetic energy  Kelvin temperature of a gas. Developed to explain gas behavior

7. 7 Kinetic Molecular Theory As the kinetic energy increases, the average velocity of the gas increases

8. 8 Kinetic Molecular Theory: Applications to Gases  As volume of a gas increases:  the KE avg of the gas remains constant.  the gas molecules have to travel further to hit the walls of the container.  the pressure decreases

9. 9 Kinetic Molecular Theory: App’s to Gases (continued)  If the temperature increases at constant V:  the KE avg of the gas increases  there are more collisions with the container walls  the pressure increases

10. 10 Kinetic Molecular Theory: App’s to Gases (continued)  effusion is the escape of a gas through a tiny hole (air escaping through a latex balloon)  the rate of effusion can be quantified

11. 11 Kinetic Molecular Theory: App’s to Gases (continued) The Effusion of a Gas into an Evacuated Chamber

12. 12  Diffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing.  Diffusion is slowed by gas molecules colliding with each other. Kinetic Molecular Theory: App’s to Gases (continued)

13. 13 Real Gases  Real Gases do not behave exactly as Ideal Gases.  For one mole of a real gas, PV/RT differs from 1 mole.  The higher the pressure, the greater the deviation from ideal behavior

14. 14 Real Gases

15. 15 Real Gases  Chemists must correct for non-ideal gas behavior when at high pressure (smaller volume) and low temperature (attractive forces become important).  The assumptions of the kinetic molecular theory show where real gases fail to behave like ideal gases:  The molecules of gas each take up space  The molecules of gas do attract each other