1 The Chemistry of Gases Unit 4 Chapter 12

2 12.1 Characteristics of GasesRead Section 12.1 p

3 Pre-assessment Title: Crushed BottleThis bottle was opened at the top of Mount San Jacinto. After it was resealed, it was then brought back down to the bottom of the mountain. Discuss with a neighbor and then write a paragraph explaining why it is crushed.

4 12.1 Atmospheric Pressure

5 See p. 422 Write a paragraph explaining what this diagram is telling us.

6 Gases Discuss and write down the names of three chemicals which are gases. 5TH, 6th Demo: Marble + acid Zinc + acid

7 Properties of gases: Gases are fluids Gases have low densityGases fill whatever container they are in Gases can be compressed Why? In a gas, the molecules are moving around quickly and randomly

8 Notes Pressure: caused by molecules striking the wall of a containerPressure = Force / Area The SI unit of pressure is the Pascal (Pa) See Fig 6 p. 419 Barometer Video clip: “Barometer – device to calculate air pressure”

9 Writing assignment Title: Barometer See Fig 6 p. 419Write a paragraph explaining how a barometer works to measure air pressure. Draw a diagram.

10 Some different units of pressure p. 420See Chem Ref Sheet: Define units

11 Pressure unit conversionConvert a pressure of 225 kPa to atmospheres. ANSWER = 2.22 atm Wanted: bring an empty soda can to class 4. end

12 Practice question Convert a pressure of 2 atmospheres to Pascals.(hint: first convert atm to KPa, then convert KPa to Pa) ANS = Pa (Extras: Convert the local pressure to Pascals) End 3. done

13 Warm-up: pressure unit conversion1. Convert 426 mm mercury pressure to Pascals (Hint: first convert mm Hg to KPa (using conversion factor on Chem Ref Sheet), then convert KPa to Pa) ANS = Pa 2.Convert Pascals pressure to mm of mercury. ANS = mm Hg

14 Pressure unit conversionClasswork p. 421 #1,2,3,4* Be prepared for a quiz on pressure unit conversions. Suggested practice extras: p. 422 # 8,9,10

15 Worksheet Kinetic Molecular Theory

16 CA Chemistry Standard 4b Students know the random motion of molecules explains the diffusion of gases.

17 6th

18 Diffusion Read p. 436 Diffusion KWS:Theprocesswhereparticlesmixastheresultoftheirrandommovement The process where particles mix as the result of their random movement Homogenous mixture: same throughout Draw it!! Sim: PhET gas properties 1. done

19 6th

20 Standard Temperature and Pressure (STP)standardtemperatureandpressure(stp)isastandardsetofconditionsforexperimentalmeasurementstoallowcomparisonstobemadebetweendifferentsetsofdata. STPis1atmospherepressureand0°C 1. done

21 STP Standard Temperature and Pressure (STP) is a standard set of conditions for experimental measurements, to allow comparisons to be made between different sets of data. STP is 1 atmosphere pressure and 0°C. p. 420

22 CA Content Standard 4c. Students know how to apply the gas laws to relations between the Pressure (P) Temperature (T) Volume (V) of any amount of an ideal gas or any mixture of ideal gases. Combined Gas Law preview

23 Warm-up In the following sentences, all the words have been joined together and the punctuation has been removed. Rewrite the definition into correct English in your notes: ‘in1662theenglishscientistrobertboylestudiedtherelationshipbetweenthevolumeandthepressureofagashefoundthatasthepressureonagasincreasesinaclosedcontainerthevolumeofthegasdecreases’

24 Warm-up ‘In 1662, the English scientist Robert Boyle studied the relationship between the volume and the pressure of a gas. He found that as the pressure on a gas increases in a closed container, the volume of the gas decreases.’

25 Think about it….. What happens to the pressure of a gas when the volume is decreased? (reminder: volume is the amount of space something takes up) The pressure increases.

26 Boyle’s Law Compression When volume decreases, pressure increasesExpansion When volume increases, pressure decreases

27 Boyle’s Law Pressure and volume are inversely (directly/inversely) proportional

28 Boyle’s Law Why? Think Kinetic Molecular Theory Sim: gas properties

29 Boyle’s Law

30 Boyle’s Law P1= initial pressure V1= initial volume P2= final pressureV2= final volume

31 Boyle’s Law Practice questionA sample of gas occupies 523 mL at 1.00atm. The volume of the gas is decreased to 265 mL, while the temperature remains the same. What is the new pressure of the gas? GIVEN: P1 = 1.00 atm V1 = 523 mL V2 = 265 mL T1 = T2 UNKNOWN: P2 = ? atm Prediction: P2 < 1.00 atm OR P2 > 1.00 atm

32 Boyle’s Law Equation Start with Combined Gas LawWhen temperature is constant T1 = T2 P1V1 = P2V2

33 Boyle’s Law Practice questionA sample of gas occupies 523 mL at 1.00atm. The volume of the gas is decreased to 265 mL, while the temperature remains the same. What is the new pressure of the gas? P1 = 1.00 atm V1 = 523 mL V2 = 265 mL T1 = T2 UNKNOWN: P2 = ? atm Now, rearrange, substitute and solve….. ANSWER = 1.97 atm

34 Boyle’s Law Practice questionsPractice: p. 425 # 1-4 Then, complete Kinetic Molecular Theory worksheet Then, can you figure out Charles’s Law on your own??? P. 428 #1-4

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36 Learning Objective Students know how to apply the gas laws to relations between the Pressure (P) Temperature (T) Volume (V) of any amount of an ideal gas or any mixture of ideal gases.

37 Charles’s Law: Think about it…..What happens to the volume of a balloon if the temperature is increased? Volume increases

38 Charles’s Law T↑ V↑ T↓ V↓ (IF pressure is held constant)V and T are directly proportional.

39 Charles’s Law

40 Charles’s Law Can be derived from Combined Gas Law, if P1 = P2T must be converted to Kelvin.

41 Charles’s Law (Can be derived from Combined Gas Law)Rearrange eqn to solve for: V2 = ? T2 = ?

42 Chem Joke Why shouldn’t you believe in atoms?Because they make up everything 

43 Charles’s Law Practice ProblemA balloon is inflated to 665 mL volume at 27°C. It is immersed in a dry-ice bath at −79°C. What is its volume, assuming the pressure remains constant? First, need to convert the temperatures to Kelvin T1 = 27oC = ?K V1 = 665 mL T2 = -79oC = ?K V2 = ? mL ANS = 430 mL

44 Charles’s Law PracticeClasswork p.428 #1-4

45 Think about it…… What happens to the pressure of a gas in a balloon if the temperature is increased? Think Kinetic Molecular theory 3,4, 5 start (what to do with early finishers?)

46 Gay-Lussac’s Law: T↑ P↑ T↓ P↓ P is directly proportional to T(IF volume is held constant)

47 Graphically…….

48 Mathematically….. Can be derived from Combined Gas LawTemperature must be in Kelvin

49 Practice question A sealed can containing gas at 101 kPa and 22oC is heated to 55oC. Calculate the pressure in the heated can (assume volume is constant) Use G.U.E.S.S. Remember: convert oC to K T1 = 22oC = ?K P1 = 101 kPa T2 = 55oC = ?K ANSWER = 112 kPa

50 G-L Law Practice p. 431 # 1-4 (Gay-Lussac's Law)Early finishers: p. 432 #5-9 1. Start with showing answer key

51 GAS LAWS Variables Equation Boyle Pressure Volume Temp P1V1=P2V2Constants Equation Propor-tionality Boyle Pressure Volume Temp P1V1=P2V2 Inverse Charles pressure V1/T1= V2/T2 Direct Gay-Lussac Pressure temp P1/T1= P2/T2

52 Avagadro’s Law in1811theitalianscientistAvagadroproposedtheideathatequalvolumesofallgasesunderthesameconditionshavethesamenumberofparticles In 1811, the Italian scientist Avagadro proposed the idea that equal volumes of all gases under the same conditions, have the same number of particles. p.431

53 Fig. 15 p.431

54 Avagadro’s Law Fig. 15 p.431 See Chemistry Reference SheetWhat is STP? What is an Ideal gas? Read p. 433

55 Puppies are cute

56 Avagadro’s Law PracticeWhat is the volume of 3 moles of gas at STP? G: moles U: volume Mol  volume conversion Conversion factor: 1 mol = 22.4L ANSWER = 67.20 L

57 Practice How many moles of gas occupy a volume of 112 L at STP?Volume  mol ANSWER = 5 mol 1,5,6. start

58 Molar volume practice How many moles of gas occupy a volume of 73.2 L at STP? Same as, how many pairs of jeans could you buy if you have $73.20 (one pair costs $22.40)? G: volume (L) U: moles Volume  mol ANSWER = 3.27 mol

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60 Practice: Gas Laws A sample of neon gas starts out at STP. What will be the pressure of the gas if the Kelvin temperature is doubled (while the volume is held constant)? ANS = 2 x 1 atm = 2 atm 1,5

61 Review What is the volume of 1 mole of carbon dioxide at STP? 22.4LWhat is the volume of 1 mole of oxygen gas at STP? 22.4 L What is the volume of 1 mole of hydrogen gas at STP? What is the volume of 1 mole of any gas at STP

62 Molar volume practice 2/19A sample of gas at STP has a volume of 8.24 L. Calculate the number of moles of gas in the sample. Same as: How much pizza can you buy if you have $8.24 and one pizza costs $22.40 ANSWER = 0.368 mol done

63 Gas stoichiometry practiceIn an experiment, we burn 10 g of carbon. What volume of carbon dioxide gas will be formed if the gas is collected at STP? p.441

64 Gas stoichiometry practiceStep 1: Given: 10 grams C Unknown: ? moles C Conversion factor: Need atomic mass of C Calculate moles of C

65 Gas stoichiometry practiceStep 2: Given: 0.83 mol C Unknown: ? mol CO2 Need balanced chemical equation for combustion of carbon Conversion factor: Need molar ratio of C:CO2 Calculate moles of CO2

66 Gas stoichiometry practiceIn an experiment, we burn 10 g of carbon. What volume of carbon dioxide gas will be formed if the gas is collected at STP? Step 3: Given: 0.83 mol CO2 Unknown: ? L CO2 Conversion factor: 1 mol = 22.4 L ANSWER = 19 L

67 Gas Stoichiometry practiceIn the combustion reaction of 149 g of propane (C3H8) with excess oxygen gas, what volume of carbon dioxide is produced at STP? Step 1: mass propane  mol propane need molar mass propane Step 2: mol propane  mol CO2 need balanced chem equation Step 3: mol CO2  volume CO2 use 22.4 L/mol ANSWER = 227 L 5, 6th

68 Gas Stoichiometry extra practiceIn the combustion reaction of 149 g of butane (C4H10) with excess oxygen, what volume of carbon dioxide is produced at STP? ANSWER = 230L 1. Assigned for h’wk – show key 1,3,5

69 Think about it? A sealed can contains a gas at 101 kPa and 300 K. It is heated to 600 K. Calculate the new pressure of the gas in the heated can (assume volume is constant) 50.5 kPa 101 kPa 202 kPa 404 kPa 1,3,4,5

70 Soda Can mini-lab What did you observe?Work in designated teams of 4; need safety glasses Pour ~40 mL of water into empty soda can Place soda can on hotplate and set hotplate to “12 o’clock position” Take your seat and wait until water is boiling vigorously (you will see steam coming out the top) ~~~~~~~~~~~~~~~~~~~~~~~ Using tongs: carefully lift can from hotplate quickly turn can upside down, and Sink open end into water bath What did you observe?

71 Soda Can mini-lab PredictWrite a sentence predicting what will happen when the soda can is inverted and submerged in the water bath. Observe Write a sentence describing your observation when the soda can was inverted and submerged in the water bath. Explain Write a paragraph explaining the science of what happened to the gas inside the can (think kinetic molecular theory)

72 Oops!!

73 Learning Objective * Students know how to solve problems by using the ideal gas law in the form PV = nRT.

74 Ideal Gas Law PV = nRT P = Pressure (atm or kPa) V = Volume (L) n = number of moles of gas R = ‘Ideal Gas Constant’ (depends upon given pressure units) T = temperature (K)

75 Ideal Gas Law PV = nRT Algebra practice- Rearrange to solve for: P = V = n = T =

76 Practice: Ideal Gas Lawp. 435 # 1-4 (P given in kPa) Green book p. 61 #1,7,9 (P given in atm)

77 Think about it…. 6

78 Warm-up: 2/20 What pressure and temperature do STP correspond to?What is the volume of 1 mole of ideal gas at STP? Convert 430K to degrees Celsius A sample of neon gas occupies a volume of 30 L at STP. What will be the temperature of the gas if the pressure is doubled (while the volume is held constant)?

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