Animated Charles and
of this slide is also available.
Air is a gas which has various
properties that we can observe with our
senses, including the gas pressure,
temperature (T), mass, and the volume (V) that
contains the gas. Careful, scientific observation has determined that
these variables are related to one another and that the values of
these properties determine the state of the
The relationship between temperature and volume, at a constant
number of moles and pressure, is called Charles and Gay-Lussac's
Law in honor of the two French scientists who first investigated
this relationship. Charles did the original work, which was verified
by Gay-Lussac. They observed that if the pressure is held constant,
the volume is equal to a constant times the temperature.
In a scientific manner, we can fix any two of the four primary
properties and study the nature of the relationship between the other
two by varying one and observing the variation of the other. This
slide shows a schematic "gas lab"
in which we can illustrate the variation of the gas properties. In
the lab a theoretical gas is confined in a blue container. The volume
of the gas is shown in yellow and is determined by the position of a
red piston. The volume can be changed by moving the red piston using
the red screw at the top of the piston. The number of moles of the
gas is indicated by the number of small black "molecules" in the
volume. The number of moles can be changed by injecting or
withdrawing molecules using the pump at the left.
The pressure can be changed by adding
or removing green weights from the top of the red piston, and the
temperature can be changed by heating the container with the "torch"
at the bottom.
There are two
probes inserted into the bottom of the container to measure the
pressure and the temperature and display the results on the gages.
As the heat is added at the bottom of the vessel,
the temperature increases and the volume increases. The relationship is plotted on
the graph at the right.
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