Chapter 7
Gases
Properties of Gases
Gas Pressure
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Gases
What gases are important for each of the
following: O2, CO2 and/or He?
A.
B.
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C.
D.
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Gases
What gases are important for each of the
following: O2, CO2 and/or He?
A. CO2
B. O2/CO2
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C. O2
D. He
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Some Gases in Our Lives
Air:
oxygen O2
argon Ar
helium He
fluorine F2
nitrogen N2
ozone O3
carbon dioxide CO2
water H2O
Noble gases:
neon Ne krypton Kr
xenon Xe
Other gases:
chlorine Cl2
ammonia NH3
methane CH4
carbon monoxide CO
nitrogen dioxide NO2
sulfur dioxide SO2
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The Nature of Gases
 Gases are compressible
Why can you put more air in a tire, but
can’t add more water to a glass full of
water?
 Gases have low densities
Dsolid or liquid = 2 g/mL
Dgas 2 g/L
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Nature of Gases
1. Why does a round balloon
become spherical when filled
with air?
2. Suppose we filled this room halfway
with water. Where would pressure be
exerted?
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Nature of Gases
 Gases fill a container completely and
uniformly
 Gases exert a uniform pressure on all
inner surfaces of their containers
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Kinetic Theory of Gases
The particles in gases
•
Are very far apart
•
Move very fast in straight lines until they
collide
•
Have no attraction (or repulsion)
•
Move faster at higher temperatures
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Barometers
760 mmHg
atm
pressure
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Learning Check G1
A.The downward pressure of the Hg in a
barometer is _____ than (as) the weight of
the atmosphere.
1) greater
2) less
3) the same
B.A water barometer has to be 13.6 times
taller than Hg barometer (DHg = 13.6 g/mL)
because
1) H2O is less dense
2) Hg is heavier
3) air is more dense than H2O
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Solution G1
A.The downward pressure of the Hg in a
barometer is 3) the same (as) the weight of
the atmosphere.
B.A water barometer has to be 13.6 times
taller than Hg barometer (DHg = 13.6 g/mL)
because
1) H2O is less dense
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Unit of Pressure
One atmosphere (1 atm)
Is the average pressure of the atmosphere
at sea level
Is the standard of pressure
 P = Force
Area
1.00 atm = 760 mm Hg = 760 torr
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Learning Check G2
When you drink through a straw you reduce
the pressure in the straw. Why does the liquid
go up the straw?
1) the weight of the atmosphere pushes it
2) the liquid is at a lower level
3) there is empty space in the straw
Could you drink a soda this way on the moon?
1) yes
2) no 3) maybe
Why or why not?
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Solution G2
When you drink through a straw you reduce
the pressure in the straw. Why does the liquid
go up the straw?
1) the weight of the atmosphere pushes it
3) there is empty space in the straw
Could you drink a soda this way on the moon?
2) no
Why or why not? Low atmospheric pressure
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Types of Pressure Units
Pressure
Used in
760 mm Hg or 760 torr
Chemistry
14.7 lb/in.2
U.S. pressure gauges
29.9 in. Hg
U.S. weather reports
101.3 kPa (kilopascals)
Weather in all
countries except U.S.
1.013 bars
Physics and
astronomy
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Learning Check G3
A. What is 475 mm Hg expressed in atm?
1) 475 atm
2) 0.625 atm 3) 3.61 x 105 atm
B. The pressure of a tire is measured as 29.4 psi.
What is this pressure in mm Hg?
1) 2.00 mm Hg
2) 1520 mm Hg
3) 22,300 mm Hg
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Solution G3
A. What is 475 mm Hg expressed in atm?
485 mm Hg
x
1 atm
= 0.625 atm (B)
760 mm Hg
B. The pressure of a tire is measured as 29.4 psi.
What is this pressure in mm Hg?
29.4 psi x 1.00 atm x 760 mmHg = 1.52 x 103 mmHg
14.7 psi 1.00 atm
(B)
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