1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Internal energy of a substance.

  1. Nov 9, 2013 #1
    Hi all, I was taught that internal energy of an ideal gas in depending on the temperature which mean during isothermal process, the change in internal energy is equal to zero. Is this statement true?

    How about the change in the internal energy of a substance when it is condensed from saturated vapour to saturated liquid isothermally?

    Sincerely thanks to those who help me :)
  2. jcsd
  3. Nov 10, 2013 #2
    No. During the condensation, it is not an ideal gas. It's part vapor and part liquid.
  4. Nov 10, 2013 #3


    User Avatar
    Science Advisor
    Gold Member

    That's true for an ideal gas, but in real gases there's a slight dependence of internal energy on volume, i.e. the partial derivative ##\left(\frac{\partial U}{\partial V}\right)_{T,n}## is not exactly zero. This is related to the Joule-Thomson effect.
  5. Nov 10, 2013 #4


    User Avatar
    Homework Helper

    yeah, for a 'true' ideal gas, the internal energy only depends on the temperature (assuming the number of molecules is constant). I think some people call this 'true' ideal gas a 'perfect' gas.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Internal energy substance Date
B Internal energy of compressed gas Jul 18, 2017
I Why triatomic gases have internal energy 7RT/2 ? Nov 14, 2016
I Internal Energy of a real gas Nov 4, 2016