Chemistry / Unit 7 Chem 1269 short lesson, about 20 seconds
Mole Fraction and Partial Pressure
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The idea
A gas's partial pressure equals its mole fraction, its moles divided by total moles, multiplied by the mixture's total pressure.
In practice
A gas making up one-quarter of a mixture's moles contributes exactly one-quarter of the mixture's total pressure.
Where people slip
Mole fraction is a ratio of moles, not of mass — a heavier gas at the same mole fraction contributes the same pressure share.
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