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Gases Part 2

Gases Part 2. Effusion and Diffusion. Diffusion - spontaneous intermingling of the molecules of one gas Effusion - gradual movement of gas molecules through a very tiny hole into a vacuum RATES of both depend on speed of gas molecules

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Gases Part 2

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  1. Gases Part 2

  2. Effusion and Diffusion • Diffusion - spontaneous intermingling of the molecules of one gas • Effusion - gradual movement of gas molecules through a very tiny hole into a vacuum • RATES of both depend on speed of gas molecules • Faster the molecules move, more rapidly diffusion and effusion occur

  3. Graham’s Law • Thomas Graham studied rates of diffusion and effusion of variety of gases • Sent through porous clay pots and small openings • At same T & P, found rates of effusion were inversely proportional to square roots of density

  4. Graham’s Law • DIFFUSION AND EFFUSION • Can compare by taking ratio of effusion rates • Also, can compare to molecular mass

  5. Graham’s Law in Use • The hydrogen halide gases all have the same general formula, HX, where X can be Cl, Br, or I. If HCl(g) effuses 1.88 times more rapidly than one of the others, which hydrogen halide is the other, HBr or HI? HX is 128 which corresponds to HI.

  6. Kinetic-Molecular Theory • Gas consists of an extremely large number of very tiny particles that are in constant, random motion. • The gas particles themselves occupy a net volume so small in relation to the volume of their container that their contribution to the total volume can be ignored. • The particles often collide in perfect elastic collisions with themselves and with the walls of the container, and they move in straight lines between collisions neither attracting nor repelling each other!

  7. Real Gases • Gases do not obey gas laws.. Why? • Gas particles do have volume • Small forces of attraction • Van der Waals equation Where V is correction to bring measure P up to the pressure an ideal gas would exert, n is the correction to reduce measured V to the volume an ideal gas would have, and a and b are van der Waal’s constant

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