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Friday 4/27

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An Introduction to Gases Chapter 13

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Kinetic Molecular Theory Postulate #1 –Gases consist of tiny particles (atoms or molecules) Postulate #2 –These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). –Gases are COMPRESSIBLE

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Kinetic Molecular Theory Postulate #3 –The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas.

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Kinetic Molecular Theory Postulate #4 –The particles are assumed not to attract or to repel each other. Postulate #5 –The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas.

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Pressure What is pressure? How is it measured? 1.mmHg (or Torr) 2.Atmospheres (atm) 3.Pascals (used in physics: 1 pascal = 1 newton per square meter) 4. psi Equivalences: 1 atm = 760 mmHg 1 atm = 101,325 Pa = kPa 1 atm = 14.7 psi

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Pressure Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643)

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Pressure Calculation What is 475 mm Hg expressed in atm? 475 mm Hg = 1 atm 760 mm Hg atm

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Daltons Law The Law of Partial Pressure The total pressure of a mixture of gases is the sum of the partial pressures of the gases in the mixture. P total = P A + P B + P C

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Temperature Scales Notice that 1 kelvin = 1 degree Celsius Boiling point of water Freezing point of water Celsius 100 ˚C 0 ˚C 100˚C Kelvin 373 K 273 K 100 K

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Calculations Using Temperature ALL gas calculations require temperature in Kelvin T (K) = T(˚C) Body temp = 37 ˚C = 310 K Liquid nitrogen = -196 ˚C = 77 K ALL gas calculations require temperature in Kelvin T (K) = T(˚C) Body temp = 37 ˚C = 310 K Liquid nitrogen = -196 ˚C = 77 K

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Relationships How are temperature and volume related? How are volume and pressure related? How are pressure and temperature related?

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Reminders Homework: Gases WS 1 Reminders: Extra Credit Due 5/11 Test Corrections due 5/1

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Monday and Tuesday 4/30 and 5/1

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Warm Up When you increase the temperature in a container, do the particles of gas move faster or slower? Would this increase or decrease the pressure? What would happen if you put a balloon in the freezer? What would happen if you put a balloon in the oven? Is it possible to compress a gas?

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Put a few drops of water in a can. Heat the can until the water boils. What is happening to the gas inside? Now flip the can over into cold water. Predict what do you predict will happen? Demo

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On a Larger Scale

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Gas Laws Calculations Get out a calculator!!!

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The Gas Law PV=nRT P = pressure ( atm or kPa ) V= volume ( L ) n= number of moles (mol) T= temperature (K)

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R – The Proportionality Constant Value depends on units L (kPa) mol (K) L (atm) mol (K) Or

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The Gas Law – Problem If 7.0 moles of an ideal gas has a volume of 12.0 L with a temperature of 300. K, what is the pressure in kPa? P (12.0 L)=(7.0 mol)(300 K)8.314 L (kPa) mol (K) PV = nRT P = kPa P = 1500 kPa

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The Gas Law – Problem If 4.00 moles of a gas has a volume of 10.0 L with a temperature of 303. K, what is the pressure in atm? P (10.0 L)=(4.00 mol)(303 K) L (kPa) mol (K) PV = nRT 9.95 atm

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Combined Gas Law Lets say we have a balloon full of O 2 gas AND we change some conditions. Would there be anything similar between the two gases?

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Combined Gas Law – Problem You have 3.0 moles of a solution at 300. K and 15 atm in a 2.0 L container. If the container is heated to 350. K and the volume decreased to 1.0 L, what will the new pressure be? P1P1 15 atmP2P2 want V1V1 2.0 LV2V2 1.0 L n1n1 3.0 molesn2n2 R1R1 constantR2R2 T1T KT2T K

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Combined Gas Law – Problemc P1V1P1V1 = n1R1T1n1R1T1 P2V2P2V2 n2R2T2n2R2T2 P1V1P1V1 = T1T1 P2V2P2V2 T2T2 If we know that R 1 = R 2 and the mass is constant then (15 atm)(2.0 L) = (300. K) P 2 (1.0L)(350. K) Replace with numbers

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Combined Gas Law – Problem (15 atm)(2.0 L) = (300. K) P 2 (1.0 L)(350. K) (15 atm)(2.0 L)(350. K) = P2P2 (1.0L)(300. K) P 2 = 35 atm

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Pressure & Volume At constant Temperature Pressure and Volume vary inversely. –Why? –More collisions More pressure P 1 V 1 = P 2 V 2 P1V1P1V1 = n1R1T1n1R1T1 P2V2P2V2 n2R2T2n2R2T2

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P & V – Example Problem If you start with L of a gas at 7.0 atm and you move the gas to a container with 3.5 L available, how much pressure will the gas exert? 7.0 atm (0.500 L) =P2P2 3.5 L P 1 (V 1 ) = P 2 (V 2 ) 7.0 atm (0.500 L) = P 2 (3.5 L) 1.0 atm = P 2

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Temperature & Volume At constant Pressure Volume & Temperature vary directly. –Why? –More collisions More Volume V1V1 = V2V2 T1T1 T2T2 P1V1P1V1 = n1R1T1n1R1T1 P2V2P2V2 n2R2T2n2R2T2

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T & V – Example Problem If a gas is in a balloon with a volume of 12.0 L and at a temperature of 300. K, what will the volume be if you place the balloon in a freezer at 250. K? V1V1 = V2V2 T1T1 T2T L = V2V K250. K 12.0 L (250. K) = V2V K 10.0 L= V2V2

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S.T.P. Standard Temperature and PressureStandard Temperature and Pressure These are conditions that are universal Standard Temperature: 0ºC or K Standard Pressure: 1atm or kPa

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S.T.P. – Example Problem What is the volume of 1 mole of a gas at STP? P1 atm Vwant n1 mole R (L)(atm)/(K)(mole) T273 K PV = nRT (1atm)V = (1 mole)( [Latm/Kmole])(273K) V= 22.4 L

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Practice Problems The pressure of a sample of gas is 5.00 atm and the volume is 30.0 L. If the volume is changed to 50.0 L, what is the new pressure?

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Practice Problems A sample of gas has a volume of 50.0 L at a temperature of 300.K. What temperature would be needed for this sample to have a volume of 60.0 L if its pressure remains constant?

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Practice Problems A 3.68g sample of a certain diatomic gas occupies a volume of 3.00 L at 1.00 atm and a temperature of 45°C. Identify this gas.

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Quiz Time Have out a pencil and a calculator

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Cage of Death Lab Determine the volume of one mole of gas at STP Do prelab before class Lab write up due

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Reminders Homework: Gases WS 2 Cage of Death Pre-lab Reminders: Extra Credit Due 5/11

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Wednesday and Thursday 5/2 and 5/3

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Warm Up A sample of gas has a volume of 90.0 L at a temperature of 303.K. What temperature would be needed for this sample to have a volume of 70.0 L if its pressure remains constant?

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Cage of Death Lab Determine the volume of one mole of gas at STP Gas collection tube Balancing pressure Making cage

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Cage of Death Lab 2. Why is the length of the magnesium ribbon important? Think back to stoichiometry. 3. Be careful with the HCl – 3.0 M is very corrosive

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Cage of Death Lab Why is it important that the HCl and H 2 O dont mix? Not too tight Not too loose

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Cage of Death Lab (F) Todays atmospheric pressure is…

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Cage of Death Lab Allow reaction to happen… How would a bubble effect your results? Too low Too highJust right

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Cage of Death Lab Repeat the lab for a second trial. CLEAN UP Liquids down drain Solids return to container

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After Lab Done in lab? Work on Homework: Cage of Death Write Up Gases WS 3 Reminders: Extra Credit due 5/11

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Friday 5/4

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Warm Up A sample of gas is in a 13.0 L container with 1.26 atm of pressure on it at 23.5 ˚C. How many moles of gas are in the sample? If the gas in the problem above is released from its container into a 56.0 L container but the temperature remains constant, what will the new pressure be?

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Demos How does atmospheric pressure affect gas particles?

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Reminders Homework: Study for your test Reminders: Extra Credit Due 5/11 Gases Test 5/7 or 5/8

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