Chapter 7 Gases

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# Chapter 7 Gases - PowerPoint PPT Presentation

Chapter 7 Gases. 7.1 Properties of Gases 7.2 Gas Pressure. 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

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## Chapter 7 Gases

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Presentation Transcript
Chapter 7 Gases

7.1 Properties of Gases

7.2 Gas Pressure

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 volumes of the containers they occupy
• have kinetic energies that increase with an increase in temperature
Properties of Gases
• Gases are described in terms of four properties: pressure (P), volume (V), temperature (T), and amount (n).
Gas Pressure

Gas pressure

• is the force acting on a specific area

Pressure (P) = force

area

• has units of atm, mmHg, torr, lb/in.2 and kilopascals(kPa).

1 atm = 760 mmHg (exact)

1 atm = 760 torr

1 atm = 14.7 lb/in.2

1 atm = 101.325 kPa

Learning Check

A. What is 475 mmHg expressed in atmospheres (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

Solution

A. What is 475 mmHg expressed in atm?

2) 0.625 atm

475 mmHg x 1 atm = 0.625 atm

760 mmHg

B. The pressure of a tire is measured as 2.00 atm. What is this pressure in mmHg?

2) 1520 mmHg

2.00 atm x 760 mmHg = 1520 mmHg

1 atm

Atmospheric Pressure

Atmospheric pressure

• is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth
Atmospheric Pressure (continued)

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
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
Learning Check

A. The downward pressure of the Hg in a barometer is _____ the pressure of the atmosphere.

1) greater than 2) less than 3) the same as

B. A water barometer is 13.6 times taller than a mercury barometer (DHg = 13.6 g/mL) because

1) H2O is less dense

2) H2O is heavier

3) air is more dense than H2O

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 mercury barometer (DHg = 13.6 g/mL) because

1) H2O is less dense