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13.6 Dalton’s Law of Partial Pressure. There are mixtures of gases almost everywhere (atmosphere, scuba gear, lab experiments) Each gas in a mixture acts like it’s the only gas One of the first people to work on this was our old pal, John Dalton. gas.
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13.6 Dalton’s Law of Partial Pressure • There are mixtures of gases almost everywhere (atmosphere, scuba gear, lab experiments) • Each gas in a mixture acts like it’s the only gas • One of the first people to work on this was our old pal, John Dalton
gas... • Dalton said, for a mixture of gases in a container, the total pressure is equal to the sum of all the partial pressures • Partial Pressure is the pressure that a gas would exert if it were all alone
called Dalton’s Law of Partial Pressures Ptotal = P1 + P2 + P3…
It really doesn’t matter what gas it is, just how much (inmoles)
If you know the mol ratios you know the pressure ratios • For this example the mol fractions are: N2 = 1.00/1.75 = 0.57O2 = 0.50/1.75 = 0.29Ar = 0.25/1.75 = 0.14 • So each contributes its share of the total P:ppN2 = 0.57 of 8.4 = 4.8 atmppO2 = 0.29of 8.4 = 2.4 atmppAr = 0.14 of 8.4 = 1.2 atm
Example • Oxygen is collected over water @ 22˚C. The total pressure of the system is 754 torr. The water vapor pressure @ 22˚ C is 21 torr. What is the pressure of the oxygen? • Ptotal = Poxygen + Pwater • Poxygen = Ptotal - Pwater • Poxygen = 754 torr - 21 torr • Poxygen = 733 torr
Example • A balloon contains both helium and nitrogen. The partial pressure of the helium is 93 torr. The total pressure inside the balloon is 101 torr. What is the pp of the nitrogen? • Ptotal = Pnitrogen + Phelium • Pnitrogen = Ptotal - Phelium • Pnitrogen = 101 torr - 93 torr • Pnitrogen = 8 torr