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Lecture11222

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a supplemental resource for students

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Transcript

  • 1. Gas State: Density, Molar Mass, Partial Pressure Lecture 11
  • 2. What about that smoke density?
  • 3. Why are this smog covering the city?
  • 4. A less dense gas will lie above a more dense one, in absence of mixing.
  • 5. The ideal gas law can be easily rearranged to calculate the density of a gas.
  • 6. Expressing ideal gas density:
    • PV=nRT
    • n=m/M (m - mass, M - molar mass)
    • PV=(m/M) x RT
    • PM=(m/V) x RT
    • m/V=d (d-density)
    • PM=dRT
    • d = PM/RT
  • 7. Two important ideas from d=PM/RT:
    • The density of a gas is directly proportional to its molar mass.
    • The density of a gas is inversely proportional to its temperature.
  • 8. A sample problem on calculating gas density.
  • 9. What allows this balloon fly?
  • 10. Expressing ideal gas molar mass:
    • PV=nRT
    • n=m/M (m - mass, M - molar mass)
    • PV=(m/M) x RT ; M=mRT/PV
    • PM=(m/V) x RT
    • m/V=d (d-density)
    • PM=dRT
    • M = dRT/P
  • 11.
    • Jean Baptiste André Dumas (1800-1884), French scientist
  • 12. A sample problem on finding the molar mass of a volatile liquid.
  • 13. Why the ideal gas law holds for any gas or mixture
    • Gases mix homogeneously (form a solution) in any proportions.
    • Each gas in a mixture behaves as it were the only gas present (assuming no chemical interactions).
  • 14.
    • John Dalton (1766-1840), British scientist
  • 15. Dalton’s law of partial pressures: in a mixture of unreacting gases, the total pressure is the sum of the partial pressures of the individual gases: P total =P 1 +P 2 +P 3 +…
  • 16. Consider air (N 2 , O 2 , Ar):
    • P N2 =n N2 RT/V
    • P O2 =n O2 RT/V
    • P Ar =n Ar RT/V
    • P total =P N2 +P O2 +P Ar
    • P total = n N2 RT/V+ n O2 RT/V+ n Ar RT/V
    • P total =(n N2 +n O2 +n Ar )RT/V=n total RT/V
  • 17. Mole fractions and partial pressures in a sample of air: X(  ); X N2 =n N2 /n total X N2 =n N2 /(n N2 + n O2 + n Ar ) P N2 =X N2 P total P O2 =X O2 P total P N2 =X Ar P total
  • 18. A sample problem on applying Dalton’s law of partial pressures.
  • 19. The water vapor depends only on the water temperature. When finding the partial pressure of a gas collected above water, we should subtract the water vapor from the total gas pressure.
  • 20. A sample problem on calculating the amount of gas collected over water.
  • 21. THE END