Gas Diffusion?

erjkism

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?

mgb_phys

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.

erjkism

k thanks

MichaelXY

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.

erjkism

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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mgb_phys Recognitions: Homework Help Science Advisor	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.

MichaelXY	Gas Diffusion? 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.

erjkism	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