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Average kinetic energy

  1. Sep 15, 2012 #1
    1. The problem statement, all variables and given/known data

    Find the average kinetic energy in kJ/mol (including all degrees of freedom) of one mole of ethane at 410K.

    2. Relevant equations

    1/2Mu^s = kT/2
    u= avg. velocity
    E=n/2kT
    N=degrees of freedom

    3. The attempt at a solution

    C2H6 degrees of freedom - 3n-6 = 18

    (18/2)(1.380x10^-23 j/k)(410K)= 5.09e^20J

    not sure how to get to KJ/mol from here.
     
  2. jcsd
  3. Sep 15, 2012 #2

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    You should first check your arithmetics. Powers of 10, to be exact. Then comes the physics.
     
  4. Sep 16, 2012 #3
    Okay, thanks for the note on converting j to kj. My main question is how do I know how many degrees of freedom to use in order to complete the equation.
    My professor sent us an equation to use:

    the total internal
    energy is (3+J)/2RT where J is the number of rotational degrees of
    freedom in the molecule.

    I calculated the degrees of freedom to be 18 due to 3n-6. But that was not correct. Do I just use the rotational degrees of freedom or all degrees of freedom? Thanks.
     
  5. Sep 17, 2012 #4
    Got it! Thanks for the help
     
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