Gas Diffusion?

  1. i did an experiment involving gas diffusion through a glass tube. HCl was on one side of the tube, while NH3 was on the other side. it took about 5 minutes for the gases to meet in the middle of the tube and form a precipitate.

    but the mean velociries of the HCL and NH3 gas molecules at 25 degrees celsius are around 500 m/s. why did it take so long for the molecules to meet and react?
     
  2. jcsd
  3. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    Most of the time the 500m/s HCL molecule is bouncing off other HCL molecules.
    Imagine a crowd where everyone is running around in circles bumbing into each other - the crowd as a whole only moves very slowly.
     
  4. k thanks
     
  5. But would not the size of the molecules also effect the transit time. Not being a wise guy, just trying to learn as well. My thinking is the NH3 would be larger, so it would be like cramming a bunch of stuff in a small hole.
     
  6. actually the HCl molecules are larger, and they ended up going quite a bit slower than the lighter NH3 molecules. It goes along with grahams diffusion rate equations
     
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