Chapter 16 section 3
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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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Chapter 16 section 3

Chapter 16 Section 3

Gas Behavior


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 = ?


Gas behavior

  • 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 = ?


Gas behavior

  • 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

    T1T2

    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


Gases are fun

Gases are fun!


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