Gas molecules follow a tortuous path which slows them down in getting from one point to another. However, the net rate at which gas molecules move in a particular direction does depend on their average speeds.
DIFFUSION
Diffusion is the migration of molecules as a result of random molecular motion. The diffusion of two or more gases results in the intermingling of molecules and in a closed container, produces a homogenous mixture.
EFFUSION
Effusion is the escape of gas molecules from their container through a tiny orifice or pinhole. The rate at which effusion occurs is directly proportional to molecular speeds. That is, molecules with high speeds effuse faster than molecules with low speeds. The following equation represents effusion:
The rate of effusion of a gas is inversely proportional to the square root of its molar mass
LIMITATIONS
Graham's law can only be used describe effusion at low pressures, so that molecules that pass through orifice are passed individually and not as jet of gas. Also, the orifice must be small enough so that no collisions occur as molecules pass through. When effusion takes place under these conditions listed above, then the equation above can be used to determine which effuses faster.
An effective way to do this is to note that in every case, a ratio of effusion rates, times, distances and so on is equal to the square root of the ratio of molar masses.
RATIO OF :
- Molecular speeds
- Effusion rate
- Effusion times
- Distance travelled by molecules
- Amount of gas effused
IS EQUAL TO : SQRT ( RATIO OF MOLAR MASSES)
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