1. Introduction to the Properties of Gases Chapter 14

2. What do you know about gases? particle Diagramsparticle Diagrams Ar(g), H 2 (g), CO 2 (g)Ar(g), H 2 (g), CO 2 (g) gases take shape & volume of their containergases take shape & volume of their container gases flowgases flow gases have low densitiesgases have low densities

3. Properties of Gases 1.gases have mass 2.gases take shape & volume of container 3.gases are compressible 4.gases easily move through each other (perfume, skunks!)  “Diffusion” 5.gases exert pressure

4. gases take shape of container Why don’t the balloons on Why don’t the balloons on the right keep expanding the right keep expanding until they pop? until they pop?

5. What is pressure? pressure = force per unit areapressure = force per unit area P = forceP = force area force = mass x acceleration Would you rather have your foot stepped on by someone wearing sneakers or stilleto heels?

6. What is air pressure? pressure exerted on us by weight of gases above our heads (& all around our body)pressure exerted on us by weight of gases above our heads (& all around our body)0 at sea level:at sea level: air pressure = 1 atmosphere air pressure = 1 atmosphere this is standard pressure

7. http://www.youtube.com/watch?v=JsoE4F 2Pb20

8. Torricelli discovered air pressure & invented mercury barometer in 1643discovered air pressure & invented mercury barometer in 1643 1 st person to propose correct explanation for wind1 st person to propose correct explanation for wind

10. reporting air pressure - take short-cut & report height of Hg column At 1 atm: column height is 29.92 in Hg or 76 cm Hg or 760 mm Hg

11. How does downward pressure of Hg in column compare to pressure of atmosphere? How does downward pressure of Hg in column compare to pressure of atmosphere?

12. Can we use H 2 O in a barometer? D Hg = 13.6 g/ml and D water = 1.0 g/ml therefore … a barometer made with water has to be 13.6 times taller than a Hg barometer () 13.6 times taller than a Hg barometer ()

13. How does air pressure at top of Mt. Whitney (14,494 ft) compare to air pressure at John Jay? What about Death Valley (86 m below sea level)?

14. When you drink through straw, you reduce pressure in straw so… Why does liquid in cup go up the straw?Why does liquid in cup go up the straw? Could you drink a soda this way on the moon? Explain why or why not?Could you drink a soda this way on the moon? Explain why or why not?

15. Units of pressure 14.7 lb/in 2 U.S. pressure gauges14.7 lb/in 2 U.S. pressure gauges 29.9 in Hg U.S. weather*29.9 in Hg U.S. weather* 101.3 kPa SI Units (Regents)101.3 kPa SI Units (Regents) (kPa = kilopascal) 1.013 BarsPhysics & Astronomy1.013 BarsPhysics & Astronomy CHEMISTRY also use: 760 Torr, 760 mm Hg, 1 atm

16. What causes the pressure of a gas in a closed container? impacts of gas molecules with walls of container anything that increases # of impacts per second or force of each impact increases pressure Microscopic View

17. light molecules move faster and hit walls more often heavy molecules hit walls with greater force these 2 effects essentially balance out **gas pressure doesn’t depend on the identity of the gas**

18. Pressure Depends on 1)concentration (# gas molecules per unit volume) (# gas molecules per unit volume) and and 2) temperature

19. How fast do the molecules in the air move? depends on massdepends on mass light molecules faster than heavy molecules at same temperaturelight molecules faster than heavy molecules at same temperature temperature = measure of average KE of particles in systemtemperature = measure of average KE of particles in system

20. Molecular Speeds at 298 K H 2 1.93 X 10 5 cm/secH 2 1.93 X 10 5 cm/sec He1.36 X 10 5 cm/secHe1.36 X 10 5 cm/sec O 2 4.82 X 10 4 cm/sec *O 2 4.82 X 10 4 cm/sec * Ar4.31 X 10 4 cm/secAr4.31 X 10 4 cm/sec Xe2.38 X 10 4 cm/secXe2.38 X 10 4 cm/sec 48200 cm x 1 in x 1 ft x 1 mile x 3600 sec = sec 2.54 cm 12 in 5280 ft 1 hour 1080 miles per hour

21. speeds of various gasses according to mass

22. Molecular Speed vs. Temperature

23. Pressure – Microscopic View gas molecules hit walls of their containergas molecules hit walls of their container pressure depends on:pressure depends on: – # impacts per unit time – Force each impact

24. Pressure – Macroscopic View pressure depends on:pressure depends on: how many (# moles) gas molecules per unit volume & how many (# moles) gas molecules per unit volume & temperaturetemperature same amount of gas exerts different pressure at different temperatures (tires)same amount of gas exerts different pressure at different temperatures (tires)

25. Describing Gas Phase System need 4 variables to completely describe gas-phase system from macroscopic (lab) view 1. pressure 2. volume 3. temperature 4. amount gas (# moles)

26. Exit Ticket name 5 common properties of all gasesname 5 common properties of all gases draw particle diagram of oxygen in gas phasedraw particle diagram of oxygen in gas phase use your particle diagram to explain at least 2 properties of gasesuse your particle diagram to explain at least 2 properties of gasesBonus: At 0 o C, a He atom is moving at 1200 m/s. How fast is this in miles per hour? Show all work!