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Chemistry 20 Chapter 4 - Gases

Chemistry 20 Chapter 4 - Gases. 4.1 Empirical Properties of Gases. Definition of a gas:. A substance that: always fills and assumes the shape of their container is highly compressible diffuses rapidly mixes readily with other gases. Gas Laws. Pressure:. a force per unit area

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Chemistry 20 Chapter 4 - Gases

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  1. Chemistry 20Chapter 4 - Gases 4.1 Empirical Properties of Gases

  2. Definition of a gas: A substance that: • always fills and assumes the shape of their container • is highly compressible • diffuses rapidly • mixes readily with other gases

  3. Gas Laws

  4. Pressure: • a force per unit area • SI unit is the kilopascal (kPa) • 1 kPa = 1000N/m2 • Atmospheric Pressure - pressure exerted by the air • Standard Pressure 1 atm = 101.325 kPa

  5. Pressure • Standard conditions for work with gases are: • STP (standard temperature and pressure) which is 0ºC and 1 atm (101.325 kPa) • SATP (standard ambient temperature and pressure) which is 25ºC and 100 kPa

  6. Boyle’s Law pressure and volume are inversely proportional. As the pressure on a gas increases, the volume of the gas decreases proportionally, provided that other variables, such as temperature and amount of gas, remain constant.

  7. Boyle’s Law • pressure (P) multiplied by the volume (V), is equal to a constant (k). • PV = k • P1V1=P2V2

  8. Charles’ Law • temperature is a measure of the average kinetic energy of the molecules in a sample • Absolute zero is the point at which there is zero kinetic energy • -273.15˚C = 0 K

  9. Temperature affects the volume and/or pressure of a gas: • if a gas is free to expand, the volume increases as the temperature increases (ex. balloon) • if a gas is not free to expand, the pressure increases as the temperature increases (ex. aerosol spray can)

  10. Charles’ Law cont. • volume of a gas and it’s temperature in Kelvin are a direct relationship • as the temperature on a sample increases, the volume increases proportionally if the pressure and amount of gas are constant.

  11. Charles’ Law cont. • can be expressed as V/T=k • V represents volume • T represents temperature (K) • k represents a constant • can also be expressed as:

  12. Combined Gas Law • Boyle’s and Charles’ Laws can be used together in Combined Gas Law • always convert temperature to K

  13. Example When 50cc of air at 100.8 kPa and 25 oC is compressed in a syringe to a volume of 20cc, what is the new pressure if the temperature does not change?

  14. Given Information

  15. Combined Gas Law Example

  16. Combined Gas Law Example

  17. Combined Gas Law Example

  18. Assignment 1) Make notes on 4.1 Properties and patterns of gases page 148-159. 2) Make notes under Boyles law about Pressure page 151-152 3) Make notes under Charles Law pages 154-155 4) Make notes on Kelvin temperature scale page 146 – 148 5) Do all practice problems and Section Review

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