Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Constant pressure and constant volume?

  1. Jun 30, 2011 #1
    Can a thermodynamic system simultaneously exist under both constant volume and constant pressure at a particular instant. I mean , when the system is under constant pressure condition, can we impose constant volume on the system. Please clear my doubt. I don't know if it's a silly question, but eating my brain.
     
  2. jcsd
  3. Jun 30, 2011 #2

    Bill_K

    User Avatar
    Science Advisor

    It's possible, but pretty uncommon. Equivalently this says that the thermal expansion (∂V/∂T)P vanishes. If you Google "zero thermal expansion" you'll find a few articles where such a material has been created. Otherwise the only time the thermal expansion vanishes is at absolute zero.
     
  4. Jun 30, 2011 #3

    cjl

    User Avatar

    Sure. It just means that you also have constant temperature.
     
  5. Jun 30, 2011 #4
    Wouldn't a sealed uncooled canister of gas, such as a helium tank at a party store, be at a constant pressure and constant volume? Or is there something else to the problem I don't see?
     
  6. Jun 30, 2011 #5
    If by "constant" you mean constant in time, the specification underlined will make it a nonsense.
    Either you mean "uniform" (that means no spatial variation) or you mean a process and not an instant.

    A process with no change in pressure or volume may be possible, for a general system. Other parameters may change. For ideal gas you may have a system which variable number of particles.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook