Chapter 6 Gases

1
Chapter 6 Gases

• 6.8
• Partial Pressure (Daltons Law)

2
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.

3
Daltons Law of Partial Pressures

• Daltons 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 P1 P2 P3 .....

4
Daltons Law of Partial Pressures

5
Illustrating Partial Pressures

6
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

0.5 mole O2 0.3 mole He 0.2 mole Ar 1.0 mole
1.0 mole N2
0.4 mole O2 0.6 mole He 1.0 mole
1.0 atm
1.0 atm
1.0 atm
7
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.

8
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?

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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

10
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

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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

12
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
13
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

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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

15
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.

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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

17
Gas Exchange During Breathing
TABLE 6.5