# Gas Behavior - PowerPoint PPT Presentation

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Chapter 16 Section 3. Gas Behavior. Pressure!. Definition of pressure is: Amount of force exerted on an area P = F/A Unit in SI: Pascal (Pa) One Pascal is one Newton force on an area 1 square meter Gases exert pressure due to KE of their particles. Boyle’s Law. Robert Boyle (1627-1691)

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Gas Behavior

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#### Presentation Transcript

Chapter 16 Section 3

## Gas Behavior

### Pressure!

• Definition of pressure is:

• Amount of force exerted on an area

• P = F/A

• Unit in SI: Pascal (Pa)

• One Pascal is one Newton force on an area 1 square meter

• Gases exert pressure due to KE of their particles

### Boyle’s Law

• Robert Boyle (1627-1691)

• Studied relationship between volume and pressure of gases

• Found: as volume goes up, pressure goes down

• Product of pressure and volume of a gas is a constant if temperature does not change

• As an equation: PV=constant

• http://www.grc.nasa.gov/WWW/K-12/airplane/Animation/frglab.html

### Boyle’s Law

• More commonly, we compare pressure and volume of the same gas

• Since PV is constant, we can say:

• P1V1 = P2V2 for any gas

• To see this in action, let’s do Math Skills Activity p 505!

### Math Skills Activity!

• A balloon has a volume of 10.0 L at a pressure of 101 kPa. What will the balloon’s new volume be if the pressure changes to 43 kPa?

• What we know:

• P1 = 101 kPa

• V1 = 10.0 L

• P2 = 43 kPa

• V2 = ?

• What equation?

• P1V1 = P2V2

• So V2 = P1V1

P2

• Put in the values!

• V2 = (101 kPa)(10.0L)

(43 kPa)

• Do the math!

• V2 = 23.488 L

• Check units and math!

### Another Problem:

• A volume of helium occupies 11.0 L at 98.0 kPa. What is the new volume if the pressure increases to 101.0 kPa?

• What do we know?

• P1 = 98.0 kPa

• V1 = 11.0 L

• P2 = 101.0 kPa

• V2 = ?

• What equation?

• P1V1 = P2V2

• So V2 = P1V1

P2

• Put in the numbers!

• V2 = (98.0 kPa)(11.0 L)

(101.0 kPa)

• Do the math!

• V2 = 10.67 L

• Check your math and units.

### Charles’ Law

• Jaques Charles (1746-1823)

• Studied relationship of temperature and volume with constant pressure

• As temperature goes up, volume increases

• Volume/Temperature is a constant

• As an equation: K = V/T

• This relationship is the basis for the Kelvin temperature scale

### Charles’ Law

• More commonly, we compare one situation to another for a gas

• V1 = V2 With constant pressure

T1T2

Temperatures must be used in Kelvins!

### Charles’ Law Problem

• If a balloon has a volume of 2.0 L at 25oC, what is the volume of the balloon at 3oC?

• What do we know?

• T1 = 25oC = 298 K

• V1 = 2.0 L

• T2 = 3oC = 276 K

• V2 = ?

### Charles’ Law Problem

• What equation?

• V1 = V2

T1 T2

So V2 = V1T2

T1

• Put in the numbers! Remember, temperature must be in Kelvins!

• V2 = (2.0L)(276 K)

(298 K)

• Solve!

• V2 = 1.85 L

• Check for math and units.

### Earth’s Atmosphere

• Earth’s atmosphere divided into 5 layers

### Earth’s Atmosphere

• Exosphere: outer layer

• Thermosphere

• Mesosphere

• Stratosphere

• Troposphere: layer we live in!

### Exosphere

• Very thin outer portion of atmosphere

• Negligible pressure

### Thermosphere

• Extends from about 90 km to about 500 km above Earth

• Very low pressure

• Very high temperatures (1000oC) in upper regions

• Gases here broken into atoms by energy from sun

• Much of X-ray and UV radiation absorbed here

• Aurora occurs in this layer

### Mesosphere

• About 50 to 85 km above Earth’s surface

• Temperatures get very cold (-25oC to -90oC)

• Air is mixed by currents

• Most meteors burn up in this layer

### Stratosphere

• Altitude of the bottom of this layer varies with latitude and season

• 16 km at equator

• 8 km at poles

• Ozone heats this layer as it absorbs UV from sun

• Very few clouds, very dry air

### Troposphere

• Layer we live in!

• From surface up to 7 to 20 km altitude

• Almost all weather occurs in this layer

• Almost all dust particles and water vapor in this layer

• This layer heated from below, so warmer at lower altitudes than higher