Gases Partial Pressure Daltons Law General Organic and

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Gases Partial Pressure (Dalton’s Law) General, Organic, and Biological Chemistry Copyright © 2010 Pearson

Gases Partial Pressure (Dalton’s Law) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1

Partial Pressure The partial pressure of a gas § is the pressure of each

Partial Pressure The partial pressure of a gas § is the pressure of each gas in a mixture § is the pressure that gas would exert if it were by itself in the container General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 2

Dalton’s Law of Partial Pressures indicates that § pressure depends on the total number

Dalton’s Law of Partial Pressures indicates that § pressure depends on the total number of gas particles, not on the types of particles § the total pressure exerted by gases in a mixture is the sum of the partial pressures of those gases PT = P 1 + P 2 + P 3 +. . . General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 3

Dalton’s Law of Partial Pressures (continued) General, Organic, and Biological Chemistry Copyright © 2010

Dalton’s Law of Partial Pressures (continued) General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 4

Total Pressure § For example, at STP, one mole of a pure gas in

Total Pressure § For example, at STP, one mole of a pure gas in a volume of 22. 4 L will exert the same pressure as one mole of a gas mixture in 22. 4 L. V = 22. 4 L Gas mixtures 1. 0 mole N 2 1. 0 atm 0. 4 mole O 2 0. 6 mole He 1. 0 mole 1. 0 atm 0. 5 mole O 2 0. 3 mole He 0. 2 mole Ar 1. 0 mole 1. 0 atm General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 5

Scuba Diving § When a scuba diver is below the ocean surface, the increased

Scuba Diving § When a scuba diver is below the ocean surface, the increased pressure causes more N 2(g) to dissolve in the blood. § If a diver rises too fast, the dissolved N 2 gas can form bubbles in the blood, a dangerous and painful condition called “the bends. ” § For deep descents, helium, which does not dissolve in the blood, is added to O 2. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 6

Guide to Solving for Partial Pressure General, Organic, and Biological Chemistry Copyright © 2010

Guide to Solving for Partial Pressure General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 7

Learning Check A scuba tank contains O 2 with a pressure of 0. 450

Learning Check A scuba tank contains O 2 with a pressure of 0. 450 atm and He at 855 mm. Hg. What is the total pressure in mm. Hg in the tank? Convert atm to mm. Hg so all pressures have the same unit! General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 8

Solution STEP 1 Write the equation for partial pressures. Ptotal = PO 2 +

Solution STEP 1 Write the equation for partial pressures. Ptotal = PO 2 + PHe 0. 450 atm x 760 mm. Hg = 342 mm. Hg = PO 2 1 atm STEP 2 Solve for the unknown Ptotal = PO 2 + PHe STEP 3 Substitute data and calculate Ptotal = 342 mm. Hg + 855 mm. Hg = 1197 mm. Hg General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 9

Learning Check For a deep descent, a scuba diver uses a mixture of helium

Learning Check For a deep descent, a scuba diver uses a mixture of helium and oxygen with a total pressure of 8. 00 atm. If the oxygen has a partial pressure of 1280 mm. Hg, what is the partial pressure of the helium? General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 10

Solution 4800 mm. Hg STEP 1 Write the equation for the sum of partial

Solution 4800 mm. Hg STEP 1 Write the equation for the sum of partial pressures. PTotal = PO 2 + PHe PTotal = 8. 00 atm x 760 mm. Hg = 6080 mm. Hg 1 atm STEP 2 Solve for the unknown partial pressure. PHe = PTotal – PO 2 STEP 3 Substitute pressures and calculate unknown. PHe = 6080 mm. Hg – 1280 mm. Hg = 4800 mm. Hg General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 11