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!

Thermodynamics Sign Problem

  1. Nov 11, 2009 #1
    1. The problem statement, all variables and given/known data
    A gas spontaneously expands into an evacuated container. Indicate whether delta T, delta E, delta H, delta S, q, w, and delta G are positive, negative, or zero.


    2. Relevant equations
    delta G < 0 (spontaneous)
    delta G= delta H - TdeltaS
    delta E= q + w
    [/B]

    3. The attempt at a solution
    delta T: 0? (Is it wrong to assume this is an isothermal reaction?)
    delta E: 0
    delta H: -
    delta S: +
    q: 0
    w: 0
    delta G: -
    Am I correct? And what difference does it make that it is in an evacuated container?
     
  2. jcsd
  3. Nov 11, 2009 #2

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It's not the best approach to assume this is an isothermal process. Can you show that's it's an isothermal process, by assuming ideality and using what you know about the change in energy?

    What's your reasoning behind delta H being negative?
     
  4. Nov 11, 2009 #3
    Hmm. If the gas is considered ideal, delta E would be zero. Since the internal E depends on T, we can assume that this is an isothermal reaction?

    Should delta H be + because added heat is needed to make the gas expand?
     
  5. Nov 11, 2009 #4

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Agreed.

    How is enthalpy defined?
     
  6. Nov 11, 2009 #5
    Enthalpy is equal to the internal Energy + PV. So is delta H=0?
     
  7. Nov 11, 2009 #6

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yep.
     
  8. Nov 11, 2009 #7
    thank you!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Thermodynamics Sign Problem
  1. Thermodynamics Problem (Replies: 4)

  2. Thermodynamics problem (Replies: 4)

Loading...