Molecular Effusion and Diffusion - Molecular Effusion and Diffusion Kinetic-molecular theory stated that The average kinetic energy of molecules is

Molecular Effusion and Diffusion - Molecular Effusion and...

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Molecular Effusion and Diffusion Kinetic-molecular theory stated that The average kinetic energy of molecules is proportional to absolute temperature Thus, at a given temperature, to different gases (e.g. He vs. Xe) will have the same average kinetic energy The lighter gas has a much lower mass, but the same kinetic energy, therefore its rms velocity (u) must be higher than that of the heavier gas where M is the molar mass Example Calculate the rms speed, u , of an N 2 molecule at room temperature (25°C) T = (25+273)°K = 298°K M = 28 g/mol = 0.028 kg/mol R = 8.314 J/mol °K = 8.314 kg m 2 /s 2 mol °K Note: this is equal to 1,150 miles/hour! Effusion The rate of escape of a gas through a tiny pore or pinhole in its container. Latex is a porous material (tiny pores), from which balloons are made Helium balloons seem to deflate faster than those we fill with air (blow up by mouth) The effusion rate, r , has been found to be inversely proportional to the square root of its molar mass: and a lighter gas will effuse more rapidly than a heavy gas: Basis of effusion The only way for a gas to effuse, is for a molecule to collide with the pore or pinhole (and escape) The number of such collisions will increase as the speed of the molecules increases
Diffusion: the spread of one substance through space, or though a second substance (such as the atmosphere)

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