1. Physical Properties Unit 5: Gases Unit 5: Gases

2. StandardsStandards b 4a. Students know the random motion of molecules and their collisions with a surface create the observable pressure on the surface b 4b. Students know the random motion of molecules explains the diffusion of gases

3. A. Kinetic Molecular Theory b Used to predict and explain the behavior of a theoretical gas or ‘ideal gas’ b 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. b ‘Ideal gases’- are elastic (do not lose energy upon collision) b Cannot be compressed given a change in temperature b Can be measured using the eq. KE= 1/2mv 2

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

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

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

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

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

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

11. b 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 b Gases can be described by their: Temperature Pressure Volume Number of molecules/moles K atm L #

13. E. Temperature ºF ºC K -45932212 -2730100 0273373 K = ºC + 273 b Always use absolute temperature (Kelvin) when working with gases!

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

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

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

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

18. G. STP Standard Temperature & Pressure 0°C 273 K 1 atm101.325 kPa -OR- STP

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

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

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