Transcript The Nature of Gases

Chapter 6
The States of Matter
6.9
Partial Pressure (Dalton’s Law)
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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.
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Dalton’s Law of Partial Pressures
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 = P1 + P2 + P3 +.....
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Dalton’s Law of Partial Pressures
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Illustrating Partial Pressures
5
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
1.0 atm
0.4 mole O2
0.6 mole He
1.0 mole
1.0 atm
0.5 mole O2
0.3 mole He
0.2 mole Ar
1.0 mole
1.0 atm
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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.
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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
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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
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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
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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
745 mmHg*0.21 = 156.4 mmHg of O2
B. At an atmospheric pressure of 714, what is the
partial pressure (mm Hg) N2 in the air?
1) 557
714 mmHg*0.78 = 556.9 mmHg of N2
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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
Gas
O2
CO2
Oxygenated
Blood
100
40
Deoxygenated
Blood
40
46
Tissues
30 or less
50 or greater
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Gas Exchange During Breathing
TABLE 6.5
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