4 ms·

Actually, according to (http://dx.doi.org/10.1063/PT.3.1796 http://dx.doi.org/10.1063/PT.3.1796) the boundary between liquid/gas and supercritical fluid is inhe

• jjoonathan 12y ago
  I'm guessing you were responding to an earlier version of my post where I kept mentioning that the liquid->supercritical and gas->supercritical boundary was poorly defined (in agreement with you) but then, in apparent contradiction to what I had just written, linked to a video of what happened at the transition, which I reconciled with my earlier claim of arbitrariness by emphasizing that the transition is well defined and physical you have a 2-phase system in equilibrium that you slide along the phase boundary until it "slips off." That's still true. You can see the evidence in the video :) But at every other point along the liquid->supercritical and gas->supercritical phase boundaries you are correct, the boundary is an arbitrary definition and not physical.
• neltnerb 12y ago
  To be slightly more specific, it is not that it is poorly defined, it is that it doesn't exist. The boundary between liquid and gas is defined by a boundary at which it requires additional energy and an accompanying abrupt change in density to change between the states. In a supercritical state, there is no additional energy or change in density. In other words, you can smoothly transition from "liquid" to "gas" without needing to boil. The two states are a single phase.