Lecture_14 - 7. Effusion and Diffusion A. Effusion Define:...

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1 7. Effusion and Diffusion A. Effusion Define : Effusion Passage of gas molecules through a tiny orifice into an evacuated chamber (vacuum). Consider the following Effusion Apparatus: • Probability of encounter of molecules at the hole is almost zero molecules effuse one by one. • Rate of effusion • At the same T : m 1 2 1 1 2 2 1 1 2 1 2 M M P P M M n n Rate Rate = = Graham’s law B. Diffusion Define : Diffusion Mixing of Gases Spread of gas molecules into a space occupied by another gas. • governed by molecular collisions, and by how much freely the gas molecules could travel. u rms (NH 3 ) = 660 m/s. Open a bottle of concentrated ammonium hydroxide. It takes a few minutes for people a few meters away to smell it !! Mean free path : λ average distance traveled between collisions. For O 2 at STP, λ≈ 1 × 10 7 m. Experiment poor diffusion in gases!
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2 • Many collisions with O 2 and N 2 molecules of the air. • We expect:
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This note was uploaded on 09/07/2010 for the course FAS chem 201 taught by Professor Sultan during the Summer '07 term at American University of Beirut.

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Lecture_14 - 7. Effusion and Diffusion A. Effusion Define:...

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