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Homework Help: Thermodynamics & Thermal Energy

  1. Dec 9, 2007 #1
    (SOLVED)Thermodynamics & Thermal Energy

    1. The problem statement, all variables and given/known data
    a 6.0m X 8m X 3m room contains air at 20 Degrees Celcius

    2. Relevant equations
    What is the room's thermal energy

    3. The attempt at a solution

    now i know that oxygen is a diatomic atom so i used

    E(thermal)= 5/2 NkbT= 5/2 nRT

    i tried to find the amount of moles by doing pv=nrt -> 5/2 pv=5/2 nRT but i don't know either the pressure exerted neither the number of moles

    so i was think to find pV i could use pV= 2/3N*[tex](\epsilon)[/tex](Average Translational kinetic energy)
    where [tex](\epsilon)[/tex]= 3/2 KbT

    so i have one question would it work like that?
    Last edited: Dec 9, 2007
  2. jcsd
  3. Dec 9, 2007 #2
    any info or help is appreciated, anything cause i have no idea if that process is right
  4. Dec 9, 2007 #3
    I am not sure, but I believe you could find n by using the volume of the room and the fact that it is at 20 Celsius.

    That is since density=mass/volume.

    I am just guessing though.

  5. Dec 9, 2007 #4

    Andrew Mason

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    Use n = PV/RT to find the number of moles. Then use:

    [tex]U = \frac{5}{2}nRT[/tex] where T = temperature in Kelvins, to find the total internal energy of the air.

    This, of course, assumes it is a perfect ideal gas so that the heat capacity of the air is 5R/2 at all temperatures which is not true.

    Last edited: Dec 9, 2007
  6. Dec 9, 2007 #5
    yeah i took a look at that but because the temperature is higher than STP i don't know density or mass
  7. Dec 9, 2007 #6

    Andrew Mason

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    You are supposed to assume that it is at atmospheric pressure. It is a room in a building, not a sealed chamber.

  8. Dec 9, 2007 #7
    WOW thanks this really helped me i didn't knew that the temperature didn't affect the atmospheric pressure, i solved it thanks
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