You will learn the difference between effusion and diffusion, and be able to calculate the difference in effusion rates of different gases.
When a person enters a room wearing a lot of a perfume, everyone knows it, beginning with the ones closest to the person and continuing to the person the furthest away. The perfume molecules mix with the other gases in the room and diffuse throughout the room. Gases being emitted from a chemical plant quickly diffuse throughout the region, and we quickly know if a paper mill is in the area - not as much so since the anti-pollution laws began affecting such emission. Diffusion of gases in the atmosphere is going on all around us all the time.
The second phenomenon studied in this section is effusion, which is the movement of gases through a porous plug of some sort between two containers at different pressures. The gases will low spontaneously (without outside help) from the region of high to the region of low pressure. Graham noted that the rate of flow of different gases was inversely proportional to the square root of their molecular weight. This observation leads us to Graham's law of effusion for the ratio of the effusion rates for two different gases. Experimental determinations of the effusion rates of two gases, one of which is an unknown gas, can lead to the determination of the molecular weight of the unknown gas.
Web Author: Dr. Leon L. Combs
Copyright ©2000 by Dr. Leon L. Combs - ALL RIGHTS RESERVED