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Chapter 10 Gases

10.1 Properties of Gases

10.2 Gas Pressure

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Kinetic Theory of Gases

A gas consists of small particles that: Move rapidly in straight lines Have essentially no attractive (or

repulsive) 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 temperature

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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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Gas pressure:• Is described as a force acting on a specific area

Pressure (P) = Force

Area• Has units of atm, mm Hg, torr, and pascals• 1 atmosphere (1 atm) is 760 mm Hg• 1 mm Hg = 1 torr

1.00 atm = 760 mm Hg = 760 torr

Gas Pressure

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Units of Pressure

Gas pressure,• Is described as a force acting on a specific area

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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 in a tire is 2.00 atm. What is this pressure in mm Hg? 1) 2.00 mm Hg 2) 1520 mm Hg 3) 22 300 mm Hg

Learning Check

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A. What is 475 mm Hg expressed in atm?2) 0.625 atm475 mm Hg x 1 atm = 0.625 atm

760 mm HgB. The pressure of a tire is measured as 2.00 atm. What is

this pressure in mm Hg?2) 1520 mm Hg2.00 atm x 760 mm Hg = 1520 mm Hg

1 atm

Solution

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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 Earth

• Is about 1 atmosphere or a little less at sea level

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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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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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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

Learning Check

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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

Solution