Describing the Properties of Gases

1. 13.1 Describing the Properties of Gases https://staff.rockwood.k12.mo.us/reedrachel/webquests/TopicWQ/19950919-McGee_large.jpg

2. Today… We are going to look at the characteristics of gases: -Pressure -Volume -Temperature -Amount http://www.treehugger.com/obama-epa-greenhouse-gases.jpg

3. What are some things gases can do? Think about hurricanes and the damage they cause. Even though we move through gases easily, they still can cause significant damage. They can exert a huge amount of pressure. http://www.secondawareness.com/wp-content/uploads/2007/01/stormglobalwarmingawareness.jpg

4. Pressure Pressure is the amount of force on a given area. Gases exert pressure on its surroundings. You can see this when you blow up a balloon; the air pushes against the sides of the balloon. http://blog.oregonlive.com/news_impact/2008/09/AndrewDahl.jpg

5. Pressure We are surrounded by air, and the air above us is pushing down on us. The air around us is exerting a lot of pressure on us. We use this pressure to our advantage. Without this pressure, our lungs would not function. (We’ll discuss this a little later.) http://www.asc-csa.gc.ca/images/spacesuit_pressure.jpg

6. Pressure Before we get into the way lungs work, we are quickly going to talk about: -how we measure pressure -units of pressure -what affects atmospheric pressure

7. Measuring Pressure To measure atmospheric pressure (the pressure due to the air around us), we use a device called a “barometer.” This is tube filled with mercury and inverted in a dish a mercury. http://ecx.images-amazon.com/images/I/41NQZ1T22GL._SL500_AA280_.jpg

8. Measuring Pressure Why does the mercury stay in the tube? The pressure from the atmosphere pushes down on the surface of the mercury in the dish, which keeps the mercury in the tube. The more pressure pushing down, the higher the mercury in the tube goes. http://www.hko.gov.hk/education/edu01met/wxobs/pressure/pres-fig2e.jpg

9. Units of Pressure Using a barometer, we saw that the more pressure there is, the higher the mercury climbs. We use the height of mercury (in millimeters) to describe the amount of pressure. The units of pressure are “mm Hg” (millimeters of mercury). http://kaffee.50webs.com/Science/images/Hg.Barometer.gif

10. Units of Pressure There are other units of pressure… -a torr - named after Torricelli, the man who invented the barometer, same thing as “mm Hg.” -a standard atmosphere (atm) - the pressure at sea level. - a pascal (Pa) = 1 N / m2 -pounds per square inch (psi) http://douggeivett.files.wordpress.com/2008/07/tire_gauge.jpg

11. Units of Pressure 1.000 atm = 760.0 mm Hg = 760.0 torr =101,325 Pa = 14.69 psi 28 psi =

12. What Affects Atmospheric Pressure? • Weather - can cause more or less air to be packed into a certain space. • Low pressure = stormy weather • High pressure = nice weather 2. Altitude - the higher you go, the less air there is pushing down on you. http://csc.gallaudet.edu/soarhigh/density.gif

13. Pressure and Volume What happens to the volume when you apply pressure to a balloon? The volume gets smaller. What happens when you open a shaken pop can? The pressure is lowered and the volume of the gases gets larger. http://www.brandchannel.com/home/image.axd?picture=2009%2F9%2Fmentos.jpg

14. Pressure and Volume Some things to notice are: When pressure increases, volume decreases. When pressure decreases, volume increases. This shows an inverse relationship between the two. http://www.antonine-education.co.uk/Physics_AS/Module_2/Topic_8/Boyle_1.gif

15. Boyle’s Law Pressure X Volume = constant P x V = k (This happens at a specific temperature and a given amount of gas) http://www.asc-csa.gc.ca/images/neemo_graph_boyles_law.jpg

16. Boyle’s Law Another way to look at things: We can see how a change in pressure will change the volume (and vice versa). P1V1 = P2V2 http://www.colorado.edu/intphys/Class/IPHY3430-200/image/17-5.jpg

17. Our Lungs use Boyle’s Law! The diaphragm’s main function is to help us breath. How does it do that? When the diaphragm expands and contracts, it is changing the volume that your lungs can hold. http://www.emptynosesyndrome.org/pics/diaphragm%20animation.gif

18. Our Lungs use Boyle’s Law! As you breath in, your lungs expand. This lowers the pressure in your lungs. Air flows from high pressure to low pressure. So if the pressure in your lungs is lower than the pressure around you, the high pressure will force air into your lungs.

19. Our Lungs use Boyle’s Law! This also explains why it is harder to breath at higher altitudes. At higher altitudes, there is enough oxygen to support you. However, there is less pressure. This means your lungs have to expand more to lower the pressure in your lungs enough for air to flow in.

20. Using Boyle’s Law Consider a 1.5 liter sample of gas at a pressure of 56 torr. If the pressure is changed to 150 torr, what will the new volume of the gas be?

21. Volume and Temperature What happens to the volume of gas when it is heated up? It expands (takes up more volume). When it is cooled down, it condenses (takes up less volume). http://bt.kieding.org/projects/watercooling/images/condensation1.jpg

22. Volume and Temperature So more heat = more volume Less heat = less volume Charles’s Law: Volume and temperature are directly proportional.

23. Charles’s Law V = bT or V / T = constant V1 = V2 T1 T2 (At constant pressure and amount of gas)

24. Using Charles’s Law: A 2.0-L sample of air is collected at 298 K and then cooled to 278 K. The pressure is held constant at 1.0 atm. What is the new volume?

25. Volume and Moles Remember, moles is just another word for “the number of particles” Think about blowing up a balloon… When you blow into it, you are putting more particles into the balloon. Then the volume increases. http://thumbs.dreamstime.com/thumb_402/1243185582BYx2NU.jpg

26. Volume and Moles The more particles, the more volume. Avogadro’s Law: The volume is directly proportional to the number of moles of gas. http://www.istockphoto.com/file_thumbview_approve/6003773/2/istockphoto_6003773-pouring-rice.jpg

27. Avogadro’s Law Volume = (some constant) x (# moles) V = a x n or V / n = constant V1 = V2 n1 n2 (At constant T and P)

28. Using Avogadro’s Law Suppose we have a 12.2-L sample of 0.50 mol of oxygen gas, O2, at 1 atm and 25oC. If all of this is converted to ozone, O3, what will the new volume be?