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Kinetic theory and
kinetic energy
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Kinetic energy is energy resulting
from motion. When dealing with billions and billions of
molecules average values are what determines the outward
properties of the sample. The kinetic energy of one molecule
is not as important as what the average value is. Average
kinetic energy is defined by the following
equation.
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KE = (1/2) x mv2
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Here the bar over the KE indicates
average kinetic energy. The "m" is the mass in kilograms and
the "v" is the velocity in meters / second.
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Kinetic molecular
theory, KMT
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The kinetic molecular theory (KMT) is a
model that does a good job of explaining the properties of
matter. The KMT applies to all three states of matter but we
will only describe how it applies to gases.
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The properties of
solids, liquids and gases are consistent with this model.
Different assumptions apply to the three states of matter.
The solid and liquid states assume intermolecular
attractions keep the particles in the condensed states. The
gas state has a series of special assumptions. these
assumptions make up the Kinetic-Molecular Theory of
Gases.
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- Gas particles are
in constant motion. Gas molecules have zero attractive
forces for other molecules.
- The average
kinetic energy of molecules is directly proportional to
the Kelvin temperature.
- Gas molecules have
negligible or zero volume compared to the volume of a gas
container.
- Gas molecules
collide like billard balls. There is no energy loss in
the collisions. The collisions are "elastic".
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These assumptions are consistent with
the observation that gases diffuse faster at higher
temperatures.
The observation that gases are
compressible agrees with the assumption that gas molecules
have a small volume compared to the container.
Billiard ball elastic collisions agree
with the observation that gases when left alone in a
container do not seem to lose energy and spontaneously
convert to the liquid.
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Note The asssumptions have
limitations. For example, gases can be liquified if cooled
enough. This means real gas molecules do attract one another
otherwise the molecules would not stick to one another and
condense.
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Dr. Walt
Volland, all rights reserved 1998-2005
revised March 31, 2005
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revised March 31, 2005