Chemistry / Unit 7 Chem 1325 short lesson, about 20 seconds
Kinetic-Molecular Theory Explains Graham's Law
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The idea
Since effusion rate tracks molecular speed and lighter molecules move faster at equal kinetic energy, kinetic-molecular theory derives Graham's inverse-square-root relationship directly.
In practice
At identical temperature, kinetic-molecular theory predicts helium's higher root-mean-square speed accounts for exactly the same rate advantage Graham's law describes empirically.
Where people slip
This derivation shows Graham's law follows from the same postulates as the other gas laws, not a separate coincidence.
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