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Molecular Effusion and DiffusionKinetic-molecular theory stated thatThe 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 gaswhere Mis the molar massExampleCalculate the rms speed, u, of an N2molecule at room temperature (25°C)T = (25+273)°K = 298°KM= 28 g/mol = 0.028 kg/molR = 8.314 J/mol °K = 8.314 kg m2/s2mol °KNote: this is equal to 1,150 miles/hour!EffusionThe 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)