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

Expansion of a Gas into a Vacuum

  1. Jan 24, 2008 #1
    1. The problem statement, all variables and given/known data
    A stop-cock which connects an evacuated flask with the atmosphere is opened and
    air at 1 atm and 17°C (290 K) enters. (a) What will be the temperature of the air in the flask
    before any heat has been transferred to the walls of the flask? Assume air to be a perfect
    gas and its molal heat capacity at constant pressure to be 7.00 calories per degree.
    Answer=132 °C (405 K)

    2. The attempt at a solution

    I started working on this under the assumption that it was a throttling question with constant enthalpy:
    H2-H1=0
    but I'm stuck at the point where you define enthalpy for each state. You can define the work done by the gas as:
    w=int(Cv dT,T,290,T2) where Cv=Cp-R (Cp=7 cal/K;Cv=5.013 cal/K)

    Any ideas on where to go?
     
    Last edited: Jan 24, 2008
  2. jcsd
  3. Jan 25, 2008 #2

    stewartcs

    User Avatar
    Science Advisor

    Sounds like a free expansion of an ideal gas problem so the temperature change will be zero, i.e. the final temp is the same as the initial temp.

    CS
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Similar Discussions: Expansion of a Gas into a Vacuum
  1. Thermal Expansion (Replies: 1)

Loading...