1. Not finding help here? Sign up for a free 30min 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- Nitrogen

  1. May 24, 2009 #1

    C.E

    User Avatar

    1. 0.005 kg of nitrogen gas (N_2 – molecular weight 0.028 kg mol-1) are heated at
    constant volume (V = 3.5 x 10^-3 m^3) resulting in a pressure increase from an initial
    value pi = 1.2 x 10^5 Pa to a final value pf = 1.8 x 10^5 Pa. Answer the following
    questions:

    (a).What are the initial and final temperatures of the gas?

    (b). What is the change in the internal energy of the gas?

    (c). What is the work done by the gas?

    (d). What is the heat flow into or out of the gas during the process?

    (e). What is the change in entropy of the gas?

    Hi, I am having trouble getting started on the above question could somebody please help me?
     
    Last edited: May 24, 2009
  2. jcsd
  3. May 24, 2009 #2

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Do you know any equations relating pressure, temperature, and volume for a gas?
     
  4. May 24, 2009 #3

    C.E

    User Avatar

    I seem to always have the same problem with this type of question. I know formulas for ideal gasses and think I could answer the question for an ideal gas but I am not told that the gas is ideal in the question. How do I know when I can assume it is ideal?
     
  5. May 24, 2009 #4

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Check if the http://en.wikipedia.org/wiki/Compressibility_factor" [Broken] is sufficiently close to 1.
     
    Last edited by a moderator: May 4, 2017
  6. May 24, 2009 #5

    C.E

    User Avatar

    When it says molar volume do you just find that by dividing the volume by the number of moles?
     
  7. May 24, 2009 #6

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes.
     
  8. May 24, 2009 #7

    C.E

    User Avatar

    How close to 1 should I take to be sufficiently close? (I really prefer them questions which say assume it behaves like an ideal gas).
     
  9. May 24, 2009 #8

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    What did it end up being?
     
  10. May 24, 2009 #9

    C.E

    User Avatar

    I couldn' t do it as I do not know the temperature of the gas. (Though thanks for the suggestion it will no doubt be useful in
    other questions).

    Should I just assume the gas is ideal anyway?
     
    Last edited: May 24, 2009
  11. May 24, 2009 #10

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The standard approach is to assume ideality, make the calculations, and then check the assumption.
     
  12. May 24, 2009 #11

    C.E

    User Avatar

    So if something similar to this comes up in my exam (this was a past exam question) would you reccommend I just assume the gas is ideal?
     
  13. May 24, 2009 #12

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

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