1.1 What is Chemistry?

http://www.ck12.org Chapter 14. The Properties of Gases

The partial pressure is the pressure that each individual gas exerts. If we assume that a certain sample of air contains
only nitrogen, oxygen, and argon, we could express the total pressure of the mixture as a sum of three partial
pressures:

Pt=PO 2 +PN 2 +PAr

Pt=total pressure

PO2=partial pressure of O 2

PN2=partial pressure of N 2

PAr=partial pressure of Ar

The percentage of the total pressure that is due to one gas in a mixture is proportional to its mole fraction. Amole
fractionexpresses what fraction or percentage the moles of a particular substance contribute to the total number of
moles present. It can be calculated as follows:

XA=total molesmolesA

Example 14.8

If you had a gas mixture that contained 3.0 moles of argon gas and 6.0 moles of oxygen gas, what is the mole fraction
of the argon? If the total pressure is 760 mm Hg, what is the partial pressure of argon?

Answer:

First, calculate the mole fraction of argon:

XAr=

moles Ar

total moles

XAr=

3 .0 moles Ar

9 .0 total moles

= 0. 33

Partial Pressure:

PAr= (XAr)(Pt)

PAr= ( 0. 33 )(760 mm Hg) =253 mm Hg

Partial Pressures and the Ideal Gas Law

We could also determine partial pressure by solving for P in PV = nRT, by using a value for n that only accounts for
one of the gases present.

Example 14.9

A gaseous mixture consists of 380 g of F 2 and 100 g of Ne. If the volume of the container is 112 L and the
temperature is 273 K, calculate:

a. The moles of each gas.

b. Total moles of all gases.

c. Mole fraction of each gas.

d. Total pressure of mixture.

e. Partial pressure of each gas.

Answer: