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Unformatted text preview: lr , L u 5.5 Dalton's Law of Partial Pressures 203 What do we know? ./ Po,
./ PTOTAL
= = 156 torr 743 torr How do we get there? The mole fraction of O2 can be calculated from the equation
• Xo,  =  Po, PTOTAL = 156 torr 743 terr = 0.210 Note that the mole fraction has no units.
SEE EXERCISE 5.85 The expression for the mole fraction,
PI Xl = P
TOTAL can be rearranged to give
PI = Xl X PTOTAL That is, the partial pressure of a particular component of a gaseous mixture is the mole fraction of that component times the total pressure. EXAMPLE 5.17 • " III The mole fraction of nitrogen in the air is 0.7808. Calculate the partial pressure of N2 in air when the atmospheric pressure is 760. torr. Solution
The partial pressure of N2 can be calculated as follows: PN,
= XN, X PTOTAL = 0.7808 X 760. torr = 593 torr
EXERCISE 5.86 SEE Collecting a Gas over Water
A mixture of gases results whenever a gas is collected by displacement of water. For example, Fig. 5.13 shows the collection of oxygen gas produced by the decomposition of solid potassium chlorate. In this situation, the gas in the bottle is a mixture of water vapor and the oxygen being collected. Water vapor is present because molecules of water escape from the surface of the liquid and collect in the space above the liquid. Molecules "," ~o.\.<e'\. 'c..~",,,'\.<e\.~"' \.'" \.\:.<e "'I."'~. W\:.""", \.\:.e 'I:.'O.\."" "'{ """',::,,'<;>'" "'''''''''''\''' \' \.b.e 'I:.",,\.e "'{ "e\.u,",,", \.h.e number of water molecules in the vapor state remains constant, and thus the pressure of water vapor remains constant. This pressure, which depends on temperature, is called the vapor pressure of water. Vapor pressure will be discussed in detail in Chapter 10. A table of water vapor pressure values is given in Section 10.8. ...
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This note was uploaded on 12/13/2010 for the course CHEM 2301 taught by Professor Bill during the Spring '10 term at South Texas College.
 Spring '10
 bill
 Organic chemistry, Mole, Partial Pressure

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