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Unformatted text preview: 1 Gases Todays Lecture 5.7 Effusion and Diffusion 5.8 Collisions of Gas Particles with the Container Walls 5.9 Intermolecular Collisions 5.10 Real Gases 5.11 Characteristics of Several Real Gases (NEW 1 SECTION: only in 6 th Edition of Zumdahl) 5.12 Chemistry in Atmosphere (omitted section; this is section 5.11 in the 5 th Edition of Zumdahl) Effusion effusion is the term used to describe passage of gas molecules through a small hole into an evacuated chamber Pinhole 2 Gas Vacuum 2 Grahams Law of Effusion Grahams law of effusion: 2 M 1 gas for effusion of rate = from kinetic molecular theory: 1 M 2 gas for effusion of rate = 1 2 2 1 avg avg M M M 8RT/ M 8RT/ 2 gas for u 1 gas for u 2 gas for effusion of rate 1 gas for effusion of rate = = = 3 note that there are limitations to Grahams law Diffusion diffusion is the term used to describe the mixing of gases note that we cannot use Grahams law to make quantitative predictions about the rates of diffusion (why?) e.g. NH 3(g) + HCl (g) NH 4 Cl (s) diffusion is slow even though the molecular velocities at 298K for HCl and NH 3 are ~450 and ~660 m/s respectively 4 the ratio predicted using Grahams law is 1.5 but the experimentally observed ratio is 1.3 (why is it different?) 1.5 17 36.5 M M u u HCl by traveled distance...
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