2. THURSDAY REVIEW Two different gases, as long as they are at the same temperature, will have the same average kinetic energy KE = ½ mv 2 (where m = mass and v = velocity) Heavier atoms/molecules move slower Diffusion – gas particles move from an area of high concentration to low concentration Effusion – the diffusion of gases through a small opening Graham’s Law is used to compare the ratio of the rates of diffusion/effusion for two different gases Ratio of rates > 1 = A is faster Ratio of rates <1 = A is slower

3. WUP #82 What is the ratio of diffusion rates for carbon dioxide (CO 2 ) and sulfur tetrafluoride (SF 4 )?

4. III. PRESSURE

5. A. WHAT IS PRESSURE?

6. B. ATMOSPHERIC PRESSURE Atmospheric pressure (air pressure) – results from collisions of air molecules with objects Air pressure is exerted by the weight of air in the atmosphere Average air pressure is 14.7 pounds per square inch (psi)

7. C. TOOLS TO MEASURE PRESSURE Barometer – device used to measure atmospheric pressure.

8. C. TOOLS TO MEASURE PRESSURE Manometer – device used to measure pressure of a gas sample

9. DOES AIR PRESSURE ONLY ACT IN A DOWNWARD MANNER?

10. HOW MUCH AIR PRESSURE IS PUSHING ON DOWN ON YOU RIGHT NOW? Recall: average air pressure is 14.7 lbs/in 2 (psi) Assume the area of the top of your head and shoulders is ~ 0.1 m 2 ~ 1.076 ft 2 ~ 155 in 2 How many pounds of pressure are pushing down on you right now? 2278.5 lbs!

11. A NISSAN VERSA!

12. WHY DO YOU NOT COLLAPSE UNDER THE WEIGHT OF ALL THAT PRESSURE?

14. THERE IS NO SUCH THING AS SUCTION…ONLY A PUSH OR A PULL

15. D. UNITS OF PRESSURE 1.Kilopascals (kPa) 2.Millimeters of mercury (mmHg) 3.torr 4.Pounds per square inch (lb/in 2 or psi) 5.Atmospheres (atm)

16. E. STANDARD PRESSURE OF GASES Measured at sea level: 1 atm = 101.3 kPa = 760 mmHg = 760 torr = 14.7 psi

17. PRESSURE UNIT CONVERSION PRACTICE 1 atm = 760 mmHg = 760 torr = 101.3 kPa = 14.7 psi Convert the following: 1.1.5 atm =kPa 2.75 kPa =mmHg 3.28.14 psi = torr