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# Ideal Gas Example Problem - Partial Pressure

## Worked Chemistry Problem

Dalton's Law can be used to determine partial pressure of a gas in a balloon.

Paul Taylor, Getty Images
Question

A balloon contains 0.1 moles of oxygen and 0.4 moles of nitrogen. If the balloon is at standard temperature and pressure, what is the partial pressure of the nitrogen?

Solution

Partial pressure is found by Dalton's Law

Px = PTotal ( nx / nTotal )

where
Px = partial pressure of gas x
PTotal = total pressure of all gases
nx = number of moles of gas x
nTotal = number of moles of all gases

Step 1

Find PTotal

Standard pressure is 1 atm

Step 2

Find nTotal

nTotal = noxygen + nnitrogen
nTotal = 0.1 mol + 0.4 mol
nTotal = 0.5 mol

Step 3

Solve for Pnitrogen

Pnitrogen = PTotal ( nnitrogen / nTotal )
Pnitrogen = 1 atm ( 0.4 mol / 0.5 mol )
Pnitrogen = 0.8 atm

The partial pressure of the nitrogen is 0.8 atm.