1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Adiabatic gas Compression of Piston after Critical Point

  1. Nov 19, 2012 #1
    Hello there,

    Sorry, if there's a thread about this already.

    Let's say if i have Piston which is fully insulated because as mentioned, it is an adiabatic compression. The pressure will increase as the volume of decrease. But what really happened when the system is compressed over the critical point. In pv diagram, will the pressure:

    a. Remain constant
    b. Increase exponentially
    c. Decrease
    d. drop to 0 in a straight line

    The temperature is assumed to be not constant.
    My idea would be 'c' or 'd' because of phase change from gas to liquid. However, I couldn't understand the kinetic theory behind it.

    Thanks for any help.
  2. jcsd
  3. Nov 19, 2012 #2


    User Avatar
    2017 Award

    Staff: Mentor

    If you compress it enough, you will run into the regime of electron degeneracy pressure, where pressure increases quickly with density.

    Why do you expect the pressure to decrease? Beyond the critical point, gas and liquid are identical, you have a high pressure (otherwise you are not beyond the critical point anyway) and temperature.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook