Transcript Chapter 2 Atoms and Elements

Chapter 11 Gases
11.1 Properties of Gases
11.2 Gas Pressure
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Kinetic Molecular Theory of
Gases
Gases consist of small particles that
• move rapidly in straight paths
• have no attractive forces
• are very far apart
• have very small volumes
compared to the volume of the
container they occupy
• have kinetic energies that increase
with an increase in Kelvin
temperature
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Atmospheric Pressure
The atmospheric pressure
• is the pressure exerted by
a column of air from the
top of the atmosphere to
the surface of the Earth
• is about 1 atmosphere or
a little less at sea level
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Properties of Gases
• Gases are described in terms of four
properties: pressure(P), volume(V),
temperature(T), and amount(n).
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Units of Pressure
Gas pressure
• is described as a force acting on a specific area
Pressure (P) = force
area
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Learning Check
A. What is 475 mmHg expressed in atm?
1) 475 atm
2) 0.625 atm
3) 3.61 x 105 atm
B. The pressure in a tire is 2.00 atm. What is this
pressure in mmHg?
1) 2.00 mmHg
2) 1520 mmHg
3) 22 300 mmHg
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Solution
A. What is 475 mmHg expressed in atm?
475 mmHg
x 1 atm
= 0.625 atm (2)
760 mmHg
B. The pressure of a tire is measured as 2.00 atm.
What is this pressure in mmHg?
2.00 atm x 760 mmHg
1 atm
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= 1520 mmHg (2)
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Barometer
A barometer
• measures the
pressure exerted by
the gases in the
atmosphere
• indicates atmospheric
pressure as the
height in mm of the
mercury column
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Units of Pressure
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Altitude and Atmospheric
Pressure
Atmospheric pressure
• depends on the
altitude and the
weather
• is lower at high
altitudes where the
density of air is less
• is higher on a rainy
day than on a sunny
day
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Learning Check
A. The downward pressure of the Hg in a barometer
is _____ than (as) the pressure of the
atmosphere.
1) greater
2) less
3) the same
B. A water barometer is 13.6 times taller than a Hg
barometer (DHg = 13.6 g/mL) because
1) H2O is less dense
2) H2O is heavier
3) air is more dense than H2O
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Solution
A.The downward pressure of the Hg in a barometer
is (3) the same (as) the pressure of the
atmosphere.
B. A water barometer is 13.6 times taller than a Hg
barometer (DHg = 13.6 g/mL) because
(1) H2O is less dense.
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