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Chapter 6 Gases

6.1 Properties of Gases6.2 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 That Describe a Gas

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, lb/in.2 and kilopascals(kPa).

1 atm = 760 mm Hg (exact)1 atm = 760 torr

1 atm = 14.7 lb/in.2

1 atm = 101.325 kPa

Gas Pressure

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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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Solution

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

760 mm Hg

B. 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

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Atmospheric Pressure

Atmospheric pressureis the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth.

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Altitude and Atmospheric Pressure

Atmospheric pressure

• is about 1 atmosphere at sea level.

• 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 than mercury.

2) H2O is heavier than mercury.

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 than mercury.

Solution