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Root mean square speed and ideal gases

  1. Dec 3, 2009 #1
    1. The problem statement, all variables and given/known data
    At 318 K and 1.04 x 10-2 atm, the density of a gas is 1.75 x 10-5 g/cm3. (a) Find vrms for the gas molecules. (b) Find the molar mass of the gas.



    2. Relevant equations
    vrms= sqrt (3RT/M)
    pV=nRT
    pM=dRT
    pV=(m/M)RT



    3. The attempt at a solution

    the main problem i am having here is units, and i am getting really frustrated, because i am a chem major, and this is chemistry!

    in order to solve for the root mean square speed, i said, based on the above relationships, RT/M = p/d

    so i plugged into vrms= sqrt (3p/d) BUT i don't know what units the density and pressure should be in to yield m/s for the final speed- i have no idea to even apply unit analysis here

    thanks!
     
  2. jcsd
  3. Dec 3, 2009 #2
    i think p - N/m^2 because: P/D = (N/m^2) / (kg/m^3) = m.N / kg. According to N's 2nd law: F = ma => N/kg = m/s^2 => m.N / kg = m.m/s^2 = m^2/s^2.
     
  4. Dec 4, 2009 #3
    okay, thanks for your help :)
     
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