Gas Behavior

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Gas Behavior - PowerPoint PPT Presentation

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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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

T1 T2

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