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Gases

Gases. GASES. manometers. pressure. Kinetic theory of gases. Units of pressure. Behavior of gases. Partial pressure of a gas. Pressure vs. volume. Pressure vs. temperature. Temperature vs. volume. Diffusion/effusion. Combined gas law. Ideal gas law. Diffusion and Effusion.

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Gases

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  1. Gases

  2. GASES manometers pressure Kinetic theory of gases Units of pressure Behavior of gases Partial pressure of a gas Pressure vs. volume Pressure vs. temperature Temperature vs. volume Diffusion/effusion Combined gas law Ideal gas law

  3. Diffusion and Effusion • Diffusion • The gradual mixing of 2 gases due to random spontaneous motion • Effusion • When molecules of a confined gas escape through a tiny opening in a container

  4. Graham’s Law

  5. Graham’s Law • Conceptual: • Lighter gases travel quicker at the same temp • Consider H2 vs. Cl2 Which would diffuse at the greater velocity?

  6. Graham’s Law • Calculating the speed of a molecule can be done using the following equation

  7. Graham’s Law • Calculate the rms speed of an N2 molecule at 25oC • Convert temp to Kelvin • MM = 28 • R= 8.314 J/mol.K ( 0.0821 x 101.3)

  8. Graham’s Law • The relative rates of diffusion of two gases vary inversely with the square roots of the gram formula masses. • Mathematically:

  9. Graham’s Law Problem • A helium atom travels an average 1000. m/s at 250oC. How fast would an atom of radon travel at the same temperature? • Solution: • Let rate1 = x rate2 = 1000. m/s • Gfm1 = radon 222 g/mol • Gfm2 = helium = 4.00 g/mol

  10. Solution (cont.) • Rearrange: • Substitute and evaluate:

  11. Applications of Graham’s Law • Separation of uranium isotopes • 235U • Simple, inexpensive technique • Used in Iraq in early 1990’s as part of nuclear weapons development program • Identifying unknowns • Use relative rates to find gfm

  12. Problem 2 • An unknown gas effuses through an opening at a rate 3.16 times slower than that of helium gas. What is the gfm of this unknown gas?

  13. Solution • Let gfm2 = x rate2 = 1 gfm1 = 4.00 rate1 = 3.16 • From Graham’s Law,

  14. Solution, cont. • Rearrange • Substitute and evaluate:

  15. WWWW we do • What is the rms speed of an He atom at 40oC

  16. The rate of effusion was measured for an unknown gas is 10 time slower than helium so • Runknown /R He = 0.1 what is the molecular mass of the unknown gas

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