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!

What is the state of matter beyond the critical point?

  1. Mar 8, 2013 #1
    Starting from a gas state and reaching the liquid state by getting around the critical point in a p-T phase diagram, what happens (qualitatively) to the molecules (or atoms)? Does a fraction of them start to form bonds?

    This concept of "indistinguishable" liquid and gas is new to me.
  2. jcsd
  3. Mar 8, 2013 #2


    User Avatar
    Science Advisor

    Goldenfeld gives the analogy that it's like two rooms, but the wall between them doesn't go all the way to the top. So whether you see "latent heat" associated with a phase transition is path dependent.

    Typically, a phase boundary is defined by a discontinuity in some equilibrium thermodynamic quantity. It is by that sort of definition that whether one encounters a phase boundary between liquid and gas is path dependent.

    There was however this interesting article in Physics Today about how dynamical quantities can provide an approximate boundary between liquid and gas above the critical point.

    What separates a liquid from a gas?
    Vadim V. Brazhkin and Kostya Trachenko
    Last edited: Mar 8, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook