Basic Relationship. PV=nRT
The Ideal Gas Law was first written in 1834 by Emil Clapeyron.
- P = Pressure which can be considered as an
Energy/Volume Relation. The more energy the gas has the higher the
pressure
- V = Volume of the container
- n = related to the number of gas molecules in
the container
- R = A number that makes all the units
work
- T = The temperature of the system (Temperature
must be in the units of Kelvin, Absolute Temperature)
We have already demonstrated that energy is
directly related to temperature. The higher the temperature the
faster molecules are moving. Molecules bouncing off the walls of a
container produces the pressure. The faster they are moving, the
harder they hit the wall, the higher the pressure.
Since Pressure can be considered a Energy/Volume,
we can determine the energy of a sealed container by multiplying the
Pressure and Volume, two values that are easily measured. We can also
measure the temperature of a system but counting the number of
molecules is impossible. We can , however, determine the number of
molecules by measuring the previously mentioned macroscopic
variables.
Demos in
Class:
The Self Inflating Balloon. A Balloon is placed in
Liquid Nitrogen, a very cold substance. The balloon becomes small as
the pressure in the balloon is decreased because the temperature is
decreasing. In this case, both Pressure and Volume are changing. The
balloon is put on the table and it reinflates itself because the
balloon is warming up, the temperature of the air inside is
increasing so the volume increases.
Dry Ice Inflator. Dry ice is placed inside a
flask. As the frozen Carbon Dioxide sublimates, turns into a gas
vapor, the gas goes into a balloon attached to the flask. This is
increasing n, the number of gas molecules in the balloon so again the
volume increases.
Boyle's Law Apparatus: The volume of a cylinder is
changed and this causes a resulting change in the pressure within the
cylinder. Since the temperature is constant, and the number of
molecules is constant, the product of (Pressure)(Volume), PV, must be
constant. Therefore as the Volume gets smaller, the Pressure must
increase.
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