Chemistry / Unit 7 Chem 1272 worked example, 60 to 90 seconds
Calculating Partial Pressures in a Gas Mixture
The idea
Calculating each gas's partial pressure in a mixture means finding each component's moles from the ideal gas law, then applying that component's own P = nRT/V to isolate its individual contribution.
In practice
A 10.0-L vessel at 35 °C (308 K) holds 2.50 × 10⁻³ mol H₂, 1.00 × 10⁻³ mol He, and 3.00 × 10⁻⁴ mol Ne. Applying PV = nRT to each gas separately gives partial pressures of about 0.0063 atm for H₂, 0.0025 atm for He, and 0.00076 atm for Ne; summing the three, by Dalton's law, gives a total pressure of about 0.0098 atm.
Where people slip
Using the mixture's total moles instead of one gas's own moles when solving for that gas's partial pressure overstates every component's individual contribution, and the three partial pressures should always sum back to the measured total.
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