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Homework Help: Temperature and Kinetic Energy question

  1. Apr 24, 2009 #1
    1. The problem statement, all variables and given/known data
    At a certain temperature a sample of oxygen has a pressure of 2.0 x 10^6 Pa, and a density of 4.0 x 10^-3 g cm^-3. Find the average speed of the oxygen molecules of the gas.

    2. Relevant equations

    Ek= 3/2kT
    Ek= 1/2mv^2

    3. The attempt at a solution
    I know that the mass of oxygen is 32 g per mole so with this i could find the mass of an individual molecule= 32 g/ 6.02 x 10^23 g
    =5.3 x 10^-26 kg
    I know P= 2.0 x 10^6 Pa

    I just dont understand what to do with the density? can somebody please help me, any help would be much aprpeciated:)
  2. jcsd
  3. Apr 24, 2009 #2


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    Science Advisor
    Homework Helper

    I think you should assume that the sample is an ideal gas.
  4. Apr 24, 2009 #3
    You can't compute the average speed form the average kinetic energy, as that would yield the the average of squared velocity and then taking the squre root does not give you the average of the absolute value (modulus) of the velocity.
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