Chapter 6 Gases 6.8 Partial Pressure (Dalton’s Law)
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.
Dalton’s Law of Partial Pressures Dalton’s Law of Partial Pressuresindicates 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 = P1 + P2 + P3 +.....
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 N2 0.4 mole O2 0.6 mole He 1.0 mole 0.5 mole O2 0.3 mole He 0.2 mole Ar 1.0 mole 1.0 atm 1.0 atm 1.0 atm
Scuba Diving • When a scuba diver dives, the increased pressure causes N2(g)to dissolve in the blood. • If a diver rises too fast, the dissolved N2 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 O2 to prepare breathing mixtures for deep descents.
Learning Check A scuba tank contains O2 with a pressure of 0.450 atm and He at 855 mm Hg. What is the total pressure in mm Hg in the tank?
Solution 1. Convert the pressure in atm to mm Hg 0.450 atm x 760 mm Hg = 342 mm Hg = PO2 1 atm 2. Calculate the sum of the partial pressures. Ptotal = PO2+ PHe Ptotal = 342 mm Hg + 855 mm Hg = 1197 mm Hg
Learning Check 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 mm Hg, what is the partial pressure of the helium? 1) 520 mm Hg 2) 2040 mm Hg 3) 4800 mm Hg
Solution 3) 4800 mm Hg PTotal = 8.00 atm x 760 mm Hg = 6080 mm Hg 1 atm PTotal = PO + PHe 2 PHe = PTotal - PO2 PHe = 6080 mm Hg - 1280 mm Hg = 4800 mm Hg
Gases We Breathe The air we breathe • is a gas mixture. • contains mostly N2 and O2 and small amounts of other gases. TABLE 6.4
Learning Check A.If the atmospheric pressure today is 745 mm Hg, what is the partial pressure (mm Hg) of O2 in the air? 1) 35.6 2) 156 3) 760 B. At an atmospheric pressure of 714, what is the partial pressure (mm Hg) N2 in the air? 1) 557 2) 9.14 3) 0.109
Solution A.If the atmospheric pressure today is 745 mm Hg, what is the partial pressure (mm Hg) of O2 in the air? 2) 156 B. At an atmospheric pressure of 714, what is the partial pressure (mm Hg) N2 in the air? 1) 557
Blood Gases • In the lungs, O2 enters the blood, while CO2 from the blood is released. • In the tissues, O2 enters the cells, which release CO2 into the blood.
Blood Gases In the body, • O2 flows into the tissues because the partial pressure of O2 is higher in blood, and lower in the tissues. • CO2 flows out of the tissues because the partial pressure of CO2 is higher in the tissues, and lower in the blood. Partial Pressures in Blood and Tissue Oxygenated Deoxygenated Gas Blood Blood Tissues O2 100 40 30 or less CO2 40 46 50 or greater
Gas Exchange During Breathing TABLE 6.5