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

Internal Energy of air

  1. Jan 20, 2007 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    I'm currently studying A2 physics and I'm stumped on a particular question within a past paper involving internal energy of air. The question is as follows:

    Estimate the internal energy of the air in a room of volume 24m^3 at a temperature of about 20˚C. Assume that the air behaves as an ideal gas at atmospheric pressure. Here are some useful formulae and data. There are several ways to make this estimate. You do NOT need to use all of the information.

    pV=nRT is the equation of state of n moles of an ideal gas
    kinetic energy of n moles of an ideal gas = 3/2 nRT

    R = 8.31 J mol^-1 K^-1
    density of air = 1.3 kg m^-3
    molar mass of air = 0.030 kg mol^-1
    atmospheric pressure = 1.0x10^5 Pa

    Internal Energy = .......................................J

    Any Ideas, Regards Tom
  2. jcsd
  3. Jan 20, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Well, how many moles of an ideal gas are there in a volume of 24m3?
  4. Jan 20, 2007 #3
    i got 22.97 mols using the info provided
  5. Jan 20, 2007 #4
    Just in general, do you know how many moles are in 1 liter of an ideal gas? And from there how many moles are one cubic meter?
    Last edited by a moderator: Jan 20, 2007
  6. Feb 12, 2007 #5
    mate a litre..(not a liter!) refers to an amount of liquid not gas and there is not a set amount of moles in a litre as the volume of gas can change with regards to pressure and temprature as shown in the equation PV/T=constant (p=pressure, V=volume, T=temprature)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook