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Volume vs temp vs pressure question

  1. Dec 12, 2003 #1
    So here is the question:
    I have a gas contained in a volume(like a sealed can). If I increase the temperature does the volume stay the same?
    If I increase the pressure, does the volume stay the same?

    It seems like it would, but I think volume is confused with "quantity", which I can see changing in all of the above circumstances.

    Thx for any help
  2. jcsd
  3. Dec 12, 2003 #2
    If you have a sealed can(none of the gas can escape) you will not see an increase in volume. I think you acn see why. If you approximate this general gas as an Ideal gas, obeying the equation of state PV=nRT, you see that if you increase the temperature in a constant volume process that the pressure must also increase (by looking at the equation PV=nRT, where V,n,R all constant)
  4. Dec 12, 2003 #3


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    How is the quantity changing if you've got a sealed can?
  5. Dec 12, 2003 #4
    Well if a person can pack more pressure in, then more molecules are entering, so more "quantity", but the volume is the same. So its more dense?
  6. Dec 12, 2003 #5
    I think you are confused with what is meant by pressure. Pressure is force per unit area (F/A), so increasing the pressure does not mean increasing the number of molecules (n). It means that the force imparted on the surface has increased. You can think of this is each molecule having more momentum so when it bounces off the container, its change in momentum is greater thus making a larger force (per newton's second law). Does that make more sense (or any at all)?
    good luck,
  7. Dec 12, 2003 #6
    Yes, I understand.
  8. Dec 15, 2003 #7


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    The "ideal gas law" is PV= NRT.

    T is the temperature (in degrees Kelvin), P is the pressure, V is volume, N the number of molecules (or mols depending on how R is taken) and R is "Boltzmann's constant". If you take a "sealed" can (so that no molecules can get in or out) then N stays the same. You can increase pressure, P, by increasing T (heat the can) while V stays constant or by decreasing V (imagine one end of the can as a plunger that can be pushed down into the can) while T remains the same (you will have to push the plunger down slowly, allowing any increase in temperature due to the energy exerted to "bleed off" to the environment around the can.
  9. Dec 16, 2003 #8
    I have an, only peripherally, related question.

    Given a container with a gas, assuming a constant internal/external pressure differential, with a hole of a particular diameter/area, what is formula to compute the rate at which the gas exits the hole.

    Assume we're talking ideal gas or air and anything else that I haven't given, but are needed.
  10. Dec 21, 2003 #9

  11. Nov 30, 2006 #10
    temp vs. Pressure

    Hi All,

    I like some of the answers and the direction that this discussion is headed, but let's add one more varible to the equation, that is needed for liquids in sealed containers:
    " Coefficient of Expansion for Liquids and Gases"

    Now, with this in mind let's think another variable related to expansion of liquids and gases in a liquid state within a sealed container ,,,, say an aerosol can filled to the top;

    Electrons + heat > Coefficent of Expansion > Possible Hydraulic pressure or vapor Pressure
  12. Dec 1, 2006 #11


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    You are 3 years too late. The ship has left the harbor.

    You might want to pay attention to the DATE of the thread and the last post.

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