"basskisser" wrote in message
om...

There are several properties of gasses that can easily be demonstrated
using liquid nitrogen.

As I clearly stated, the ideal gas laws apply as long as you are NOT
operating in the temperature/pressure ranges that will result in a phase
change for the elements involved. For the pressure and temperature that a
tire will be exposed to the gas laws apply. Once you start talking about
liquid nitrogen we are clearly in the phase change realm.

You may also notice though that they will also expand a bit faster
than the heavier gasses.

No. They have a lower boiling point, and thus as you watch them react with
the surroundings they will start boiling sooner.
It takes a significant amount of engergy to make an element/compond change
state. Start with a mixture of elements/componds (assuming that they don't
react and form a new compond) that are all cooled below any of their boiling
points (the insertion into the liquid nitrogen) and then start adding energy
(remove it from the nitrogen, it absorbs energy from the surrounding air).
Track the temperature of the mixture over time. You will see a fairly rapid
and linear rise in temperature until it reaches a temperature where one of
the elments/componds changes state. At this point the temperature will
remain constant until all of the element has changed state. The temperature
will increase linearly again until the next state change temperature is
reached.

If you are comparing the rate at which such an experiment will inflate a
balloon, then a mixture that has an element/compond that changes state at a
lower temperature will certainly start inflating sooner and do it more
rapidly. This isn't a function of the gas, it is a function of the stage
change.

The differences in the expansion rate becomes
even more obvious if argon is available. Argon has a very small
difference between the freezing point and boiling point (4o C) thus an
argon filled balloon will expand very rapidly.


All elements/compounds expand as they transition into the gaseos state.
This is not universally true for the transition from solid to liquid. Many
elements/compounds, including water, have a "triple point", a
temperature/pressure combination that will allow all three phases to exist
at the same time. Predicting the exact expansion rates of a mixture where
multiple state changes are involved is a bit more tedious, although the
expansion between solid and liquid would be dramatically less than between
liquid/solid and gas.



Compare this to a
breath filled balloon or a balloon filled with a gas such as ethane

Stay above the boiling point of ethane and these two will behave the same.
Heat both balloons the same amount and they will both expand the same
amount.

Now, there is one characteristic that might lead you to a false conclusion,
and that is the rate at which the change occurs. If you took the two
balloons from a cool room into a warm room you might see one of the balloons
expand faster than the other. Leave them there until they reach
equilibrium, however, and they will both expand the same. This is due to
the thermal resistance. Just like aluminum heats up faster than iron.

Back to what I have been saying all along: PV=nRT. It works for the
temperatures and pressures that a tire will be operated at. It doesn't
matter what the gas is. If the volume stays constant, and you change the T
by x%, you change the pressure by x%. It is basic gas law, you should
have learned this in high school chemistry class.