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Physical Properties

Unit 5: Gases. Physical Properties. Standards. 4a. Students know the random motion of molecules and their collisions with a surface create the observable pressure on the surface 4b. Students know the random motion of molecules explains the diffusion of gases.

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Physical Properties

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  1. Unit 5: Gases Physical Properties

  2. Standards • 4a. Students know the random motion of molecules and their collisionswith a surface create the observable pressureon the surface • 4b. Students know the random motion of molecules explains the diffusion of gases

  3. A. Kinetic Molecular Theory • Used to predict and explain the behavior of a theoretical gas or ‘ideal gas’ • Particles in an ideal gas… • have no volume or elastic collisions • in constant, rapid, random, straight-line motion • don’t attract or repel each other

  4. ‘Ideal gases’- are elastic (do not lose energy upon collision) • Cannot be compressed given a change in temperature • Can be measured using the eq. KE= 1/2mv2

  5. B. Real Gases • Particles in a REAL gas… • have their own volume • attract each other • Gas behavior is most ideal… • at low pressures • at high temperatures • in nonpolar atoms/molecules

  6. C. Characteristics of Gases • Gases expand to fill any container • Random constant motion, no attraction • very low densities

  7. C. Characteristics of Gases • can be compressed given a change in Temp/Pressure State Changes

  8. Diffusion • The movement of one material through another. • The rate depends on the mass of the particles • Lighter = rapid diffusion

  9. Effusion • When a gas escapes through a tiny opening • Rate of effusion can be calculated according to Graham’s law of effusion: Rate of effusion = 1/SQRT MM

  10. Effusion • Using Graham’s Law, you can also set up a proportion to compare the diffusion rates for two gases • ** see eq on board.

  11. Ammonia has a molar mass of 17.0 g/mol; hydrogen chloride has a molar mass of 36.5 g/mol. What is the ratio of their diffusion?

  12. D. Describing Gases • Gases can be described by their: • Temperature • Pressure • Volume • Number of molecules/moles • K • atm • L • #

  13. E. Temperature K = ºC + 273 ºF -459 32 212 ºC -273 0 100 K 0 273 373 • Always use absolute temperature (Kelvin) when working with gases!

  14. F. Pressure Which shoes create the most pressure?

  15. F. Pressure • Barometer • measures atmospheric pressure • exact height of the Hg depends on atmospheric pressure • usually measured in mm Hg

  16. F. Pressure • Manometer • measures contained gas pressure • Difference in height in two arms of U-tube is measure of pressure of gas sample • measured in various different units

  17. F. Pressure • KEY EQUIVALENT UNITS 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi

  18. G. STP Standard Temperature & Pressure 0°C273 K 1 atm101.325 kPa -OR- STP

  19. H. Pressure Problem 1 • The average pressure in Denver, Colorado, is 0.830 atm. Express this in (a) mm Hg and (b) kPa. 760 mm Hg (a) 0.830 atm = 631 mm Hg 1 atm 101.325 kPa (b) 0.830 atm = 84.1 kPa 1 atm

  20. H. Pressure Problem 2 • Convert a pressure of 1.75 atm to kPa and mm Hg. 101.325 kPa (a) 1.75 atm = 177 kPa 1 atm 760 mm Hg (b) 1.75 atm = 1330 mm Hg 1 atm

  21. H. Pressure Problem 3 • Convert a pressure of 570. torr to atmospheres and kPa. 1 atm (a) 570 torr = .750 atm 760 torr 101.325 kPa (b) 570 torr = 76.0 kPa 760 torr

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