Diffusion Effusion and Grahams Law of Diffusion What

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Diffusion, Effusion, and Graham’s Law of Diffusion

Diffusion, Effusion, and Graham’s Law of Diffusion

What is diffusion? n The movement of particles from regions of higher concentrations to

What is diffusion? n The movement of particles from regions of higher concentrations to regions of lower concentration. n Eventually, the particles will disperse evenly throughout the space. Low High

What is effusion? n The passage of a gas under pressure through a tiny

What is effusion? n The passage of a gas under pressure through a tiny opening.

Graham’s law of diffusion n Thomas Graham studied effusion in detail and determined that

Graham’s law of diffusion n Thomas Graham studied effusion in detail and determined that the rate of effusion is indirectly proportional to the square root of the molar mass of the gas, if pressure and temperature are kept constant. n In other words: v. A v. B = Molar Mass. B Molar Mass. A

How does that work? n Let’s go back to the Kinetic Molecular Theory n

How does that work? n Let’s go back to the Kinetic Molecular Theory n We saw that the movement of particles is proportional to the amount of kinetic energy. n KE= ½ m v 2 n So, if the KE is constant, ½ m. A v. A 2 = ½ m. B v. B 2 n With a little algebra, we get: v. A v. B = Molar Mass. B Molar Mass. A

Example Problems n At the same temperature, which molecule travels faster, O 2 or

Example Problems n At the same temperature, which molecule travels faster, O 2 or N 2? How much faster? n At room temperature, Xe atoms have an average speed of 240 m/s. At the same temperature, what is the speed of H 2 molecules? n What is the molar mass of a gas if it diffuses 0. 907 times the speed of argon gas?

Answers 1) N 2 (lower molar mass) (32/28) = 1. 07 times faster 2)

Answers 1) N 2 (lower molar mass) (32/28) = 1. 07 times faster 2) x/240 = (131. 3/2) x/240 = 8. 10 x = 1944 m/s 3) 1/0. 907 = (x/39. 9) (1/0. 907)2 = ( (x/39. 9))2 1. 216 = x/39. 9 x = 48. 5 g/mol