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Homework Help: Increase gas pressure in unchanged volume

  1. Jan 13, 2008 #1


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    Start pressure: p1=1 bar;
    Volume: V=36m3;
    Temp.: T1=T.

    Now I need to increase the pressure to 6 bar, but the volume remains unchanged. So:
    End pressure: p2=6 bar;
    Volume: V=36m3;
    Temp.: T2=T.

    So volume and temperature remain unchanged.

    What amount of gas (m3) do I need to add to increase the pressure with 5 bar (p2-p1).

    Compressor gives 185 l/s, max. working pressure is 7 bar.

    I know p*V/T=p*V/T but I'm struggling to calculate the required volume.

  2. jcsd
  3. Jan 13, 2008 #2

    Shooting Star

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    You haven't given any calculations of your own. Anyway, think of the ideal gas law in its exact form. I hope you are right about the two temps being the same.
  4. Jan 13, 2008 #3


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    Gold Member

    Try ignoring the numbers for the compressor and imagine the container only.
  5. Jan 14, 2008 #4
    Any calculations you make will have to take into account STP or Standard Temperature and Pressure. You also have to know that to raise the pressure in a fixed volume container will also raise the temperature. But then after you have raised the pressure, and the temp went up with it, the pressure will drop as you let the compressed gas cool to the original temp. The whole thing is a dynamic system in which changing any one factor will change the other two.

    First you have to understand STP so follow this first link for a tutorial.


    Converting all calculations to STP after the fact gives you a basis to make comparisons.

    Another helpful tutorial is the one on an "Ideal Gas" and you can find it at the next link


    Finally you are missing one factor in your question and that is the term "mole" which refers to the absolute quantity of gas in any fixed volume system at any temperature and pressure.

    The next link is to a calculator to allow you to figure out all the info you needto know to achieve your goal.

    Last edited: Jan 14, 2008
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