# Daltons Law P total = P 1 + P 2 + P 3 +.... Daltons Law The pressure of each component is called the partial pressure of that component.

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Daltons Law P total = P 1 + P 2 + P 3 +...

Daltons Law The pressure of each component is called the partial pressure of that component.

Daltons Law For example: If we have a flask containing nitrogen gas, whose partial pressure is.78 atm and oxygen gas, whose partial pressure is.20 atm, the total pressure in the flask is P total = P N2 + P O2 P total =.78 +.20 =.98 atm

Daltons Law Another way to think about this is through the use of the mole fraction. The mole fraction is rather like calculating the percent of each component.

Daltons Law The mole fraction is written as follows a N2 = moles N 2 total moles total moles This is basically the percent (by number) of some element.

Daltons Law We can rearrange Daltons Law to use the mole fraction as follows: P x = a x (P total ) Or specifically: P N2 = a N2 (P total )

Daltons Law For example: ordinary air contains 78.084% nitrogen. We might be interested in knowing what the partial pressure of nitrogen is in the atmosphere.

Daltons Law The mole fraction of N 2 must be.78084, so P N2 =.78084(P total ) If the atmospheric pressure is 640 torr, P N2 =.78084(640) = 500 torr

Composition of Air 78.084%Nitrogen 20.948%Oxygen.934%Argon.0315%Carbon dioxide.001818%Neon.000524%Helium.000114%Krypton.0000087%Xenon

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