Chemistry / Unit 7 Chem 1300 short lesson, about 20 seconds
Graham's Law of Effusion
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The idea
A gas's rate of effusion is inversely proportional to the square root of its molar mass.
In practice
Helium, far lighter than oxygen, effuses through a pinhole several times faster than oxygen does under identical conditions.
Where people slip
The ratio of effusion rates scales with the square root of the inverse molar-mass ratio, not with molar mass directly.
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