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Gas Diffusion
 
This model illustrates the process of gas diffusion through a tube of variable diameter.
Diffusion is a spontaneous process of intermingling of molecules as a result of random thermal agitation, and their even distribution throughout a given volume. Diffusion advances the system to the state of thermodynamic equilibrium.

Consider two different gases with the same temperature and under the same pressure that are situated at the opposite ends of a vessel. If there is no barrier between the gases, molecular thermal motion will lead to permeation of molecules of both gases throughout the entire volume of the vessel. This process is known as diffusion.
The intensity of diffusion is the function of molecular free path length, i.e. the mean distance run by a molecule between two consecutive collisions with other molecules. Diffusion can be very slow if the free path length is significantly less than the dimension of a vessel.
Transmission of molecules from one vessel to another through a connecting pipe is also known as diffusion. In this case, the speed of this process strongly depends on the geometrical shape and dimensions of the connecting pipe, and on the surrounding temperature.
Observe the process of diffusion of two gases via a connecting pipe. Note the dependence of the rate of diffusion on the pipe's diameter.

 
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