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Announcements Final: Monday, April 6, 7:30 am (ugh!) 300 pts comprehensive, multiple choice, Scantron, 10% No-calc bonus Very strict exit policy!
Title: Announcements 1 Announcements
  • Final Monday, April 6, 730 am (ugh!)
  • 300 pts comprehensive, multiple choice, Scantron, 10 No-calc bonus
  • Very strict exit policy!
  • Buy Scantron Now and fill out your name and other info before coming!
  • 2 Heres what people said they learned. 3 Heres what people said they wanted to know better. 4 Tequila (dont YOU drink it) b-damascenone gives tequila some of its woody/fruity flavor 5 Chapter 11Gases what if there were no intermolecular forces? 6 At a molecular level, the states of matter differ primarily by the level of cohesion.
  • Solids (examples a penny, ice, glass???)
  • Molecules have attracted each other
  • Atoms that are bound together by sea of electrons
  • Sometimes in a specific array (crystals)
  • Sometimes not (glasses)
  • Hold their own shape indefinitely
  • Liquids (example honey, water, glass???)
  • Molecules have attracted each other
  • permanent or temporary dipoles.
  • Not in any pattern (exception liquid crystals)
  • Have a surface adopt shape of bottom of container
  • Gases (example air, helium in balloon)
  • Molecules not attracted to each other (or weakly attracted)
  • No pattern
  • No surface adopt shape of all of the container.
  • 7 How things are Everything wiggles, only some things translate. Solids molecules or atoms can wiggle about fixed, central location. They dont translate far. Liquids molecules or atoms move along (translate) until they bounce into something, and this happens frequently because the molecules or atoms have cohesion. Gases like liquids, only collisions not as often. No cohesion. 8 How fast? Depends on molecule. isopentyl acetate, CH3COOCH2CH2CH(CH3)2 About 500 miles per hourpretty fast! Lets measure it. 9 How do we KNOW that structure? 10 Why it took so long to get to back of room collisions! The isopentyl acetate molecule only goes about 200 nm before hitting something, which then sends it in a different direction. It takes forever for it to spread around the room..unless there is a draft. 11 Diffusion 10000 steps forward and 10001 steps backward The hydrodynamic world of diffusiondominated by collisionsis very different from our normal ballistic world. An object set into motion comes almost immediately to a stop, rather than coasting as we are used to seeing. 12 Gasespressure matters! Gas particle hits a piston, imparts a force. With a small number of gas atoms in the cylinder, this force would be quite random. With a large number, the force would be quite steady. We usually see almost perfectly steady pressure because there are billions of billions of particles in any normal sample. 13 You could measure pressure this way, but its pretty darn inconvenient. We still show it because its conceptually easy. P F/A mg/p r2 Mass of bricks 9.8 m/s2 Radius of piston 14 Slightly more practicalusing water height to measure pressure
  • How high will the water rise?
  • depends on the weather
  • depends on whether you're in Louisiana
  • or Colorado
  • is always a little more than 30 feet
  • Why? Because that is how far
  • atmospheric pressure can push it.
  • The vacuum pump doesn't suck
  • the air pushes.
  • 15 Yeah, but how far will the water rise? Patm rgh 101,325 nt/m2 9.8 m/s2 16 Rather than use the Super Hoover, we could draw a hose full of water, sealed at one end, out of the swimming pool.
  • Fill a hose with water, taking care to introduce no bubbles.
  • Put the hose in a large tub of water.
  • Seal one end of the hose.
  • Drag the sealed end out with a pulley.
  • When the hose tip exceeds about 34 feet, you will see the water goes no higher! You get an air gap at the top of the hose.
  • You now have a barometer. As weather changes, the height of the column of water will fluctuate.
  • 17 BOB Big Ol Barometer 18 Remember P rghso h P ? rg Denser liquids mean shorter barometers! Mercury density 13.6 g/mL Why mercury is a liquid http//antoine.frostburg.e du/chem/senese/101/periodic/faq/why-is-mercury-liq uid.shtml http// 97/862179191.Ch.r.html 19 Experiments with barometers 1 Pressure vs. temperature at fixed volume put barometer into fixed, rigid box and raise temperature. Make pressure readings. 20 Kelvin concepts T (K) T(oC) 273.15 Room temperature 25oC 298K Ice water 0.00 oC 273.15 K Boiling water 100.00 oC 373.15 K All evidence suggests that NOTHING can be colder than 0K -273.15 C If T is in Kelvins, P is directly proportional to T. You can make a barometer into a thermometer! 21 Experiments with barometers 2 Pressure vs. volume at fixed temperature put barometer into horror chamber with descending ceiling. Keep at same Temperature while ceiling lowered. Make pressure readings. Movable ceiling! Lets you change room volume. 22 P increases with inverse of volume 23 Experiments with barometers 3 Pressure vs. mass of gas at fixed T and V. More gas particles (e.g., weigh in more gas) leads to more pressure, other things (like T and V) being equal. Where N is the number of gas particles 24 Combined gas law usually called the ideal gas law Combine 25 We can rearrange that The constant is called the gas constant. This relation only works for ideal gases (but most gases are ideal). 26 The ideal gas law is good for handling transitions in closed systems. Before State 1 After State 2 (example low T) (example high T) 27 Suppose a gas is at 1.5 atm of pressure and occupies 250 mL. If the pressure is reduced to 0.5 atm, what volume does the gas now occupy? 28 765 mL of a gas is held in a container at a pressure of 0.95 atm. With temperature held constant, the pressure is decreased to 0.82 atm. What is the new volume? 29 Ideal gas law is PVnRT. But number of moles, n, is grams, g, divided by Mwt.. So 30 765 mL of a gas is held in a container at a pressure of 0.95 atm. With temperature held constant, the pressure is decreased to 0.82 atm. What is the new volume? 31 Standard Temperature Pressure (STP) is arbitrarily set at T 0oC 32oF 273.15K P 1 atm 101,325 Pa (1 Pa 1 nt/m2) 1 mol of a simple gas occupies 22.4 liters at STP 16 g CH4 22.4 liters 44 g CO2 22.4 liters 32 g O2 22.4 liters 28 g N2 22.4 liters http// /08/03/dear-milk-man/ 32 Mixing Gases, Partial Pressures Gases can mix. When they do, their pressures add (almost)   Patmospheric PO2 PN2 PH2O PAr PCO2 minor pressures from trace gases Air is approximately 80 N2, 20 O2 33 Wonderful things, everywhere you look! Water crystals exclude the grape stuff (color and sugar and flavor to make beautiful and tasty popsicle-like treat. PE Container H-CH2n-H 34 (No Transcript)
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