Kinetic Model
Kinetic Model


Review
Review
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Molecules behave independently
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Volume of particles is insignificant
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Particles travel in straight lines until
collisions change direction
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Particles have no effect on each other
except to collide
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Distribution of Speeds
Distribution of Speeds
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Kinetic model says average kinetic
energy determined by temperature
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It doesn’t mean that every molecule has
the same speed
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It’s the average that’s fixed by the
temperature
Different kinds of averages (see later)
<E
k
> = ½m<v>
2
= 3/2RT
u=(3RT/M)
1/2
Maxwell Distribution
Maxwell Distribution
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Diffusion and effusion
Diffusion and effusion
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When substances mix, the process is called
diffusion
tends to be a slow process
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When one or more substances escape through a
permeable barrier, it is called effusion
He leaking out of a balloon is effusion
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Both processes depend on temperature and molar
mass
Time inversely proportional
Rate directly proportional
A
B
A
B
B
A
M
M
t
t
r
r
=
=