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Diffusion_and_Effusion_Internet

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					 Diffusion, Effusion, and
Graham’s Law of Diffusion
           What is diffusion?
 The movement of particles from regions of
  higher concentrations to regions of lower
  concentration.
 Eventually, the particles will disperse
  evenly throughout the space.
                                 Low


    High
            What is effusion?
   The passage of a gas under pressure
    through a tiny opening.
     Graham’s law of diffusion
 Thomas Graham studied effusion in detail
  and determined that the rate of effusion is
  indirectly proportional to the square root
  of the molar mass of the gas, if pressure
  and temperature are kept constant.
 In other words:

    vA

    vB
           =        Molar MassB
                     Molar MassA
          How does that work?
 Let’s go back to the Kinetic Molecular Theory
 We saw that the movement of particles is
  proportional to the amount of kinetic energy.
 KE= ½ m v 2
 So, if the KE is constant, ½ mA vA2 = ½ mB vB2
 With a little algebra, we get:
     vA

     vB
            =        Molar MassB
                      Molar MassA
         Example Problems
 At the same temperature, which molecule
  travels faster, O2 or N2? How much
  faster?
 At room temperature, Xe atoms have an
  average speed of 240 m/s. At the same
  temperature, what is the speed of H2
  molecules?
 What is the molar mass of a gas if it
  diffuses 0.907 times the speed of argon
  gas?
                  Answers
1) N2 (lower molar mass)
(32/28) = 1.07 times faster

2) x/240 =  (131.3/2)
x/240 = 8.10
x = 1944 m/s

3) 1/0.907 = (x/39.9)
(1/0.907)2 = ((x/39.9))2
1.216 = x/39.9
x = 48.5 g/mol

				
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