Kinetic theory and non ideal gases
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Kinetic theory and non ideal gases






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Kinetic theory and non ideal gases Kinetic theory and non ideal gases Presentation Transcript

  • Kinetic Theory of Gases and Non-Ideal Gases
  • Kinetic Theory of Gases An Attempt to Explain Why the Gas Laws Work
  • Origin of the postulates of the Kinetic Theory of Gases
  • Origin of postulates part 2
  • Molecular Motion of Gases
    • Far apart
    • Free from one another
    • Randomly moving
    mean free path : average distance traveled between collisions typically ~ 10 -5 cm molecular size ~ 10 -8 cm diffusion: irregular motion of molecules
  • Velocity of gas molecules and Mean free path
  • Rotating disk method of measuring velocity distribution
  • Maxwell-Boltzmann distribution of molecular speeds same gas (N 2 ) at different temperatures
  • Maxwell-Boltzmann distribution of molecular speeds different gases at same temperature
  • Graham’s Law of Effusion Effusion is the leaking of a gas through a small hole. A Hydrogen fountain illustrating the high diffusion rate of H 2 gas. Diffusion is related but not identical to effusion.
  • The collection of a gas over water using a pneumatic trough. This method should not be used for gases that dissolve in water (then use Hg like Priestley).
  • Dalton’s Law of Partial Pressures
  • Representative partial pressures (in torr) in inhaled and exhaled air. In the respiration process, we use O2 and emit CO2 as well as humidifying the air that passes through our lungs. A corollary of Dalton’s Law is P total = X A P = mole fraction of gas A times the partial pressure of gas A
  • Gay-Lussac’s Law of Combining Volumes
  • Avogadro’s Hypothesis
  • Non-Ideal Gases Real gases condense to a liquid. An ideal gas cannot.
  • A British term for what we call UHF, Ultra High Frequency View Modern view
  • Air Liquefier
  • Dewar flask (or thermos bottle)
  • The Compressibility Factor, PV/nRT
  • Real Gases
    • Deviation from “Ideal” Gas Law
    • PV = nRT
    • for an ideal gas at STP, 1 mole = 22.414 L
    • Experimental Data
    • 1.0000 mole of gas
    • Gas Volume (L) Deviation from Ideality
    • H 2 22.433 +0.085 %
    • He 22.434 +0.089 %
    • N 2 22.404 - 0.045 %
    • O 2 22.397 - 0.076 %
    • CO 2 22.260 - 0.687 %
    • NH 3 22.079 - 1.495 %
  • Properties of Real Gases
  • Properties of Real Gases Decrease due to Intermolecular Attractive Forces Increase due to Molecular Volume significant
  • The destructive effect of higher temperatures
  • Van der Waals’ equation which corrects for the non-ideal properties of gases
  • Correcting for Deviations from Ideal Gases
    • for ideal gas: PV = nRT (Ideal gas law)
    • for “real” gas:
    • (P real + a n 2 )(V real – nb) = n RT
    • V 2
    attractive force correction molecular volume correction Van der Waals’ Equation
  • The a and b factors in Van der Waals’ equation
  • Table continued
  • Two calculations
  • Solution of the Van der Waals equation to find the Critical Temperature and Critical Pressure
  • Liquid Nitrogen Air that is so cold that it becomes a liquid (probably the coolest stuff you will ever see)
  • Liquid Nitrogen Ice Cream