# Diffusion_and_Effusion_Internet by xiaoyounan

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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?
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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