1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fnding the rms speed of hydrogen

  1. Dec 9, 2011 #1
    1. The problem statement, all variables and given/known data

    The rms speed of nitrogen molecules in air at some temperature is 493 m/s. What is the rms speed of hydrogen molecules in air at the same temperature?



    2. Relevant equations

    Vrms


    3. The attempt at a solution
     
  2. jcsd
  3. Dec 9, 2011 #2

    Delphi51

    User Avatar
    Homework Helper

  4. Dec 9, 2011 #3
    Finding the rms speed of hydrogen

    1. The problem statement, all variables and given/known data

    The rms speed of nitrogen molecules in air at some temperature is 493 m/s. What is the rms speed of hydrogen molecules in air at some temperature?


    2. Relevant equations

    root-mean-square speedvrms= [itex]\sqrt{v2}[/itex]=[itex]\sqrt{\frac{3kT}{m}}[/itex]



    3. The attempt at a solution

    mnitrogen=[itex]\frac{28.0 g}{6.02 X 1023}[/itex]=4.65 X 10-26

    mhydrogen=[itex]\frac{2.0 g}{6.02 X 1023}[/itex]= 3.32 X 10-27

    493= [itex]\sqrt{\frac{(3)(1.38 X 10-23)(T)}{4.65 X 10-26}}[/itex]
    T= 233 K

    Vrms of hydrogen= [itex]\sqrt{\frac{(3)(1.38 X 10-23(T)}{3.32 X 10-27}}[/itex]=340.43 m/s

    The answer is actually 1840 m/s.

    What did I do wrong?
     
  5. Dec 9, 2011 #4

    Delphi51

    User Avatar
    Homework Helper

    Wow, all that work and it didn't come out right!
    Better to just think for a bit. The atomic mass for the H2 is lighter by a factor of 14.
    So the 3kT/m will be 14 times larger for the hydrogen. And its square root will be sqrt(14) times larger.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Fnding the rms speed of hydrogen
  1. RMS Speed (Replies: 3)

  2. Rms speed (Replies: 4)

Loading...