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Chapter 5: GASES Part 2

Chapter 5: GASES Part 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:

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Chapter 5: GASES Part 2

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  1. Chapter 5: GASES Part 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: PTotal = P1 + P2 + P3 + . . .

  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. 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: Ptotal = Pgas + Pwater

  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 O2 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. Kinetic Molecular Theory Developed to explain gas behavior • Gases consist of a large number of molecules in constant motion. • Volume of individual particles is  zero. • Collisions of particles with container walls cause pressure exerted by gas. • Particles exert no forces on each other. • Average kinetic energy  Kelvin temperature of a gas.

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

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

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

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

  12. Kinetic Molecular Theory: App’s to Gases (continued) • 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.

  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. Real Gases

  15. Real Gases • 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 • Chemists must correct for non-ideal gas behavior when at high pressure(smaller volume) and low temperature(attractive forces become important).

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