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Friday 4/27. An Introduction to Gases Chapter 13.

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Presentation on theme: "Friday 4/27. An Introduction to Gases Chapter 13."— Presentation transcript:

1 Friday 4/27

2 An Introduction to Gases Chapter 13

3 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

4 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.

5 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.

6 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

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

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

9 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

10 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

11 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

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

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

14 Monday and Tuesday 4/30 and 5/1

15 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?

16 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

17 On a Larger Scale

18

19 Gas Laws Calculations Get out a calculator!!!

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

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

22 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

23 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

24 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?

25 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

26 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

27 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

28 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

29 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

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

31 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

32 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

33 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

34 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?

35 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?

36 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.

37 Quiz Time Have out a pencil and a calculator

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

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

40 Wednesday and Thursday 5/2 and 5/3

41 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?

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

43 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

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

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

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

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

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

49 Friday 5/4

50 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?

51 Demos How does atmospheric pressure affect gas particles?

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


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