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March 29, 2017

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Oxygen (O2) has a molar mass of 32.0 g/mol [.032kg/mol].

What is the root-mean-square speed of an oxygen molecule at a temperature of 310 K?
Vrms=492 m/s

What is its average translational kinetic energy at that speed?
Kav= ?? J


I am having problems with the second half, finding the Kav...

  • Physics - ,

    You can get Kav by calculating
    (1/2) M [Vrms]^2.

    You can also get it from the general rule
    Etr,average = (3/2) kT
    where k is Boltzmann's constant, 1.38*10^-23 Joule/K. It applies to all molecules.

  • Physics - ,

    Here is what I've done, hopefully you can identify where I've gone wrong..

    =(1/2)(.032)(492)^2
    =3873J

  • Physics - ,

    Since when is the mass of an O2 molecule .032 kg?
    You missed it by a very large factor. .032kg is aobut one ounce, which would be a very large molecule...

  • Physics - ,

    ok, that makes much more sense...

    then i'm assuming that:n=2 for O2 and the m is .032 ????
    M=n*m
    =2*.032
    =.064

    Then
    (1/2)(.064)(492)^2
    =7746 ??????

  • Physics - ,

    The question is for ONE oxygen molecule. 0.032 kg is the mass of a MOLE of oxygen molecules.

  • Physics - ,

    I am beyond lost..I've never had any chemistry and our professor assumed that we had at least a basic knowledge...is there any way you could walk me thought this?

  • Physics - ,

    No, for I've forgotton what little physics I knew at one time; however, you know (from your chemistry if not physics) that 1 mol of oxygen (0.032 kg) contains 6.02 x 10^23 molecules. So how much does 1 molecule weigh? The problem is asking for 1 molecule, not 6.02 x 10^23 molecules.

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