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I. Physical Properties

Ch. 12 - Gases. I. Physical Properties. A. Kinetic Molecular Theory. Particles in an ideal gas… have no volume have elastic collisions are in constant, random, straight-line motion don’t attract or repel each other have an avg. KE directly related to Kelvin temperature. B. Real Gases.

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I. Physical Properties

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  1. Ch. 12 - Gases I. Physical Properties

  2. A. Kinetic Molecular Theory • Particles in an ideal gas… • have no volume • have elastic collisions • are in constant, random, straight-line motion • don’t attract or repel each other • have an avg. KE directly related to Kelvin temperature

  3. 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

  4. C. Characteristics of Gases • Gases expand to fill any container • random motion, no attraction • Gases are fluids (like liquids) • no attraction • Gases have very low densities • no volume = lots of empty space

  5. C. Characteristics of Gases • Gases can be compressed • no volume = lots of empty space • Gases undergo diffusion & effusion • random motion

  6. D. 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.

  7. E. Pressure Which shoes create the most pressure?

  8. E. Pressure Mercury Barometer • Barometer • measures atmospheric pressure • exact height of the Hg depends on atmospheric pressure • usually measured in mm Hg

  9. E. Pressure U-tube Manometer • 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

  10. E. Pressure • KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi

  11. Graham’s law of effusion states that the rate of effusion for a gas is inversely proportional to the square root of its molar mass. • Graham’s law also applies to diffusion.

  12. Gas Pressure • Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases of the mixture. • The partial pressure of a gas depends on the number of moles, size of the container, and temperature and is independent of the type of gas.

  13. Ptotal = P1 + P2 + P3 +...Pn • Partial pressure can be used to calculate the amount of gas produced in a chemical reaction.

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

  15. G. 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

  16. G. 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

  17. G. 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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