1 Chapter 6 Gases 6.8 Partial Pressures (Dalton’s Law) Copyright © 2009 by Pearson Education, Inc.

2 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. Partial Pressure

3 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. P T = P 1 + P 2 + P Dalton’s Law of Partial Pressures

4 Copyright © 2009 by Pearson Education, Inc.

5 For example, at STP, 1 mole of a pure gas in a volume of 22.4 L will exert the same pressure as 1 mole of a gas mixture in 22.4 L. V = 22.4 L Gas mixtures Total Pressure 0.5 mole O mole He 0.2 mole Ar 1.0 mole 1.0 mole N mole O mole He 1.0 mole 1.0 atm Copyright © 2009 by Pearson Education, Inc.

6 Scuba Diving When a scuba diver dives, the increased pressure causes N 2 (g) to dissolve in the blood. If a diver rises too fast, the dissolved N 2 will form bubbles in the blood, a dangerous and painful condition called "the bends." Helium, which does not dissolve in the blood, is mixed with O 2 to prepare breathing mixtures for deep descents. Copyright © 2009 by Pearson Education, Inc.

7 Learning Check A scuba tank contains O 2 with a pressure of atm and He at 855 mmHg. What is the total pressure in mmHg in the tank? Copyright © 2009 by Pearson Education, Inc.

8 Solution 1. Convert the pressure in atm to mmHg atm x 760 mmHg = 342 mmHg = P O 2 1 atm 2. Calculate the sum of the partial pressures. P total = P O 2 + P He P total = 342 mmHg mmHg = 1197 mmHg

9 For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of 8.00 atm. If the oxygen has a partial pressure of 1280 mmHg, what is the partial pressure of the helium? 1) 520 mmHg 2) 2040 mmHg 3) 4800 mmHg Learning Check

10 3) 4800 mmHg P Total = 8.00 atm x 760 mmHg = 6080 mmHg 1 atm P Total = P O + P He 2 P He = P Total - P O 2 P He = 6080 mmHg mmHg = 4800 mmHg Solution

11 Gases We Breathe The air we breathe is a gas mixture. contains mostly N 2 and O 2, and small amounts of other gases. Copyright © 2009 by Pearson Education, Inc.

12 A. If the atmospheric pressure today is 745 mmHg, what is the partial pressure (mmHg) of O 2 in the air? 1) ) 156 3) 760 B. At an atmospheric pressure of 714, what is the partial pressure (mmHg) N 2 in the air? 1) 557 2) 9.143) Learning Check

13 A. If the atmospheric pressure today is 745 mmHg, what is the partial pressure (mmHg) of O 2 in the air? 2) 156 B. At an atmospheric pressure of 714, what is the partial pressure (mmHg) N 2 in the air? 1) 557 Solution

14 Blood Gases In the lungs, O 2 enters the blood, while CO 2 from the blood is released. In the tissues, O 2 enters the cells, which releases CO 2 into the blood. Copyright © 2009 by Pearson Education, Inc.

15 Blood Gases In the body, O 2 flows into the tissues because the partial pressure of O 2 is higher in blood, and lower in the tissues. CO 2 flows out of the tissues because the partial pressure of CO 2 is higher in the tissues, and lower in the blood. Partial Pressures in Blood and Tissue Oxygenated Deoxygenated Gas BloodBlood Tissues O or less CO or greater

16 Gas Exchange During Breathing Copyright © 2009 by Pearson Education, Inc.