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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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pressure
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
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 law1
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
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 = ?
slide6

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
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 = ?
slide8

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
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 law1
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
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 problem1
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
  • Earth’s atmosphere divided into 5 layers
earth s atmosphere1
Earth’s Atmosphere
  • Exosphere: outer layer
  • Thermosphere
  • Mesosphere
  • Stratosphere
  • Troposphere: layer we live in!
exosphere
Exosphere
  • Very thin outer portion of atmosphere
  • Negligible pressure
thermosphere
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
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
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
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
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