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Gas Behavior

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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  1. Chapter 16 Section 3 Gas Behavior

  2. 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

  3. 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

  4. 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!

  5. 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 = ?

  6. 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!

  7. 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 = ?

  8. 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.

  9. 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

  10. 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!

  11. 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 = ?

  12. 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.

  13. Earth’s Atmosphere • Earth’s atmosphere divided into 5 layers

  14. Earth’s Atmosphere • Exosphere: outer layer • Thermosphere • Mesosphere • Stratosphere • Troposphere: layer we live in!

  15. Exosphere • Very thin outer portion of atmosphere • Negligible pressure

  16. 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

  17. 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

  18. 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

  19. 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

  20. Gases are fun!

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