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Kinetic Theory and Gases

Kinetic Theory and Gases. Kinetic Theory. Explains how temperature and pressure affect the motion of molecules. http://exploration.grc.nasa.gov/education/rocket/Images/state.gif. Hydraulics. http://library.thinkquest.org/C007574/media/brake1.gif.

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Kinetic Theory and Gases

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  1. Kinetic Theory and Gases

  2. Kinetic Theory Explains how temperature and pressure affect the motion of molecules http://exploration.grc.nasa.gov/education/rocket/Images/state.gif

  3. Hydraulics http://library.thinkquest.org/C007574/media/brake1.gif http://csumc.wisc.edu/cmct/ParkStreetCT/locations/idealbodyshop/car.jpg http://www.hydraulic-equipment-manufacturers.com/gifs/hydraulic-lift.jpg

  4. KE—Kinetic Energy Energy of motion Depends on: • Mass • Velocity

  5. PE—Potential Energy Stored Energy • Gravitational Potential Energy Energy due to height above earth 2) Chemical Potential Energy Energy stored in bonds of batteries, food, gasoline, etc.

  6. Ideal Gases Particles are point masses—they have no volume Particles have no mutual attraction to each other Behavior of ideal gases is a model for how real gases behave Ideal Gas calculations are simple and the results are close to those for real gases

  7. Three Assumptions of Kinetic Theory • All matter is made of particles 2) Particles are in constant motion • All collisions are perfectly elastic (molecules do not lose energy in collisions)

  8. Oxygen Gas • At 25oC, average speed = 443 m/s (1000 mph) • Between collisions, an oxygen molecule travels 314 times its diameter • There are 4.5 billion collisions each second

  9. Pressure Air Pressure: the weight of air over an area Standard Pressure: average normal air pressure at sea level = 760 mmHg = 1 atm = 14.7 lbs/in2 = 101.3 kPa

  10. What Causes Gas Pressure? number and intensity of collisions -- speed of particles (temperature) -- concentration of particles -- mass / size of particles

  11. 760mm Barometer Used to measure air pressure The weight of a column of mercury is balanced by the weight of the air http://umpgal.gsfc.nasa.gov/www_root/homepage/uars-science/UARS_brochure/JPEGs/barometer.jpg

  12. Evangelista Torricelli http://www.forestry-suppliers.com/images/200/5491_w2.jpg

  13. How is Pressure related to Weather?

  14. chips chips chips chips http://www.met.utah.edu/jhorel/html/mesonet/lessons/pres_mtn.gif http://www.visionlearning.com/library/modules/mid107/Image/VLObject-2362-031023021035.gif How is Pressure related to Altitude?

  15. Pvap Pvap P atm P atm P atm Pvap t = 0 min t = 5 min BOILING! t = 1 min Boiling Pvap= Patm

  16. Boiling • The boiling point of water in Oregon is usually about ____________ • Is Oregon above or below sea level? (~974 feet above sea level) Record High : 815 mmHg Record Low: 656 mmHg <100oC

  17. Try These 101.3 760 1 atm = ________ mmHg = ________ kPa 2.1 atm = _____mmHg 0.8 atm =_____mmHg 798 mmHg = _____atm 684 mmHg =_____atm 750 mmHg = _____kPa 790 mmHg =_____kPa 1596 608 1.05 0.9 105.3 99.97

  18. Demonstrations Crush the can Vacuum pump (shaving cream, marshmallow, balloon) Tube with cap Flask with index card Gas can Air pressure – mat, glass square, well plate, soda suction Mustard container Balloon in Flask Fire Syringe Syringe/Martian Popping Thing Bernoulli bag/ball in funnell Hero’s Fountain

  19. 100 K 273 K 500 K 273 K # of molecules Kinetic Energy Temperature Average Kinetic Energy of particles in a substance (depends on the speed and mass of particles) 100 K 500 K

  20. Temperature Scales http://www.rain.org/~mkummel/stumpers/08oct99a.gif Water Boils Kelvin: Absolute temperature scale Cannot have a negative Kelvin temperature 0 K = Absolute Zero Water Freezes oC + 273 = K

  21. Practice Problems • Convert to Kelvin 23oC = _____ K -11oC = _____ K 32 oF = _____ K • Convert to Celsius 315 K = _____ oC 277 K = _____ oC 212 oF = _____ oC 296 262 273 42 4 100

  22. STP • Standard Temperature and Pressure 0oC 1 atm

  23. Diffusion • What is diffusion The random movement of particles through a medium

  24. 5 Factors that Affect the Diffusion Rate of Gases • Mass of Particles ↑ mass, ↓ rate of diffusion • Concentration of Particles ↑ conc, ↑ rate of diffusion • Temperature ↑ temp, ↑ rate of diffusion • Air Pressure ↑ Pair, ↓ rate of diffusion • Presence of Another Gas Another gas, ↓ rate of diffusion

  25. Lightestmolecule

  26. = = 3.74 Compare the relative rate of diffusion of H2 & N2 = H2 diffuses 3.74 times faster (further) than N2

  27. VNH3 36.5 VNH3 MHCl = = 17 MNH3 VHCl VHCl Lab 40 What is the relative rate of diffusion of NH3 to HCl? 1 m NH3 HCl NH3(g) + HCl (g)  NH4Cl (s) = 1.5 times faster/further

  28. The pressure of a gas is inversely proportional to its volume (when temperature is constant) P X V = k (constant) P1 V1 = P2 V2 Initial Final USE COMMON UNITS FOR P AND V!!! (both atm, kPa; or both L, ml, cm3) V P Boyle’s Law Robert Boyle 1627-1691

  29. V1 P1 ?V2 P2 Try This • You have 1000 ml of gas at 754 mmHg. Find the volume at standard pressure. P1 V1 = P2 V2 (754 mmHg)(1000ml) = (760 mmHg)V2 760 mmHg 760 mmHg V2 = 992.1 ml

  30. Partial Dalton’s Law Total pressure = sum of partial pressures Ptotal = dPgas 1 + dPgas 2 + dPgas 3 + … Pair = dPN2 + dPO2 + dPH2O etc.

  31. Pair Ptotal Pressure of “dry gas” Air Pressure Use Periodic Table Gases collected over water over water Gases collected contain water vapor H2O + O2 lower bottle until water levels are equal Ptotal = dPH2O + dPgas

  32. H2O Vapor Gas Pressure of “dry gas” From Periodic Table 750 mmHg Ptotal = PH2O + dPgas Pair

  33. Vapor Pressure Chart on PT dPH2O changes with water temp Ex: A sample of H2 is collected at 25oC and the pressure is 775 mmHg. What is the pressure of the “dry gas”? over water

  34. V1 Pvap— Periodic Table Ptotal ?V2 Example 2 80 ml of gas are collected at 22oC. The air pressure was 758 mmHg. Find the volume of dry gas at standard pressure. over water P2 P1

  35. = KELVIN Charles’ Law The volume of a gas is directly proportional to the absolute temperature (Kelvin) if the pressure is held constant V T (K)

  36. Apparently, oil tank rail cars are cleaned by scouring them with steam. Unfortunately, someone shut the hatch too soon...

  37. Try This #1 If you had 100 ml of a dry gas at 30oC, what volume would it occupy at 60oC? V2 = 109.9 ml

  38. Try This #2 350 ml of gas at 0oC is compressed to 100 ml. What is the new temperature?

  39. Graham’s Law Quiz 1) 2) 3)

  40. Open Container Increase Temp? # collisions? Pressure? Volume? Closed Container Increase Temp? # collisions? Pressure? Volume? Open vs Closed Containers

  41. V 8) 9) Ptotal = dPgas1 + dPgas2 10) Inverse Proportion 11) Direct Proportion 12) 13) “collected over water” 14) balloon in ice 15) compressed syringe T Guess the Gas Law • An eqn with V and T • An eqn with P and V • “find the pressure of the dry gas” • Uses vapor pressure of water • PV = k P V

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