2 The Atmosphere an “ocean” of gases mixed together Composition nitrogen (N2)…………..~78%oxygen (O2)……………~21%argon (Ar)……………...~1%Trace amounts of:carbon dioxide (CO2)…~0.04%He, Ne, Rn, SO2,CH4, NxOx, etc.water vapor (H2O)…….~0.1%
3 Depletion of the Ozone Layer O3 depletion is caused by chlorofluorocarbons (CFCs).Ozone (O3) in upper atmosphereblocks ultraviolet (UV) light from Sun.UV causes skin cancer and cataracts.Uses for CFCs:CFCsrefrigerants-- banned in U.S. in 1996aerosol propellantsO3 is replenished with each strike of lightning.
4 Ozone Hole Grows Larger Ozone hole increased 50% from
5 Monthly Change in Ozone TOMS Total Ozone Monthly Averages
6 Greenhouse Effect Some heat (IR) lost to outer space Light from the sun:UV, viz, IRLight is absorbed by Earth and re-radiated into theatmosphere as heat (IR)Greenhouse gases absorb heat (IR), and radiate it back into the atmosphereGLOBAL WARMINGRadiant energy from the sun enters the Earth’s atmosphere and is reflected off the surface of Earth back to outer space. The carbon dioxide and other gases in the atmosphere trap the radiant heat from leaving. This is like a greenhouse – where the glass allows the light energy in but traps the heat from escaping. Recall, when you go to your car in the winter on a sunny day. The interior of the car is warm. On a summer day the car is too hot inside if you don’t leave a window rolled down slightly to allow the heat to escape (heat rises).Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 392
7 Greenhouse Gases GREENHOUSE GASES Carbon dioxide is responsible for trapping heat on planet earth. Trees and plants naturally absorb excess carbon dioxide from the atmosphere. In the last 100 years we have removed many forest and the level of global carbon dioxide is increasing. The net effect is global warming…El Nino and La Nina, floods, drought and extreme weather patterns.
8 Why more CO2 in atmosphere now than 500 years ago?burning of fossil fuelsdeforestation--coal--urban sprawl--petroleum--wildlifeareas--natural gas--wood--rain forests*The burning of ethanolwon’t slow greenhouse effect…C2H5OH + O2 CO2 + H2O
9 Carbon Dioxide Levels Atmospheric CO2 (ppm) Year 350 300 250 1000 1500 2000YearZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 310
10 What can we do? insulate home; run dishwasher full; avoid temp. extremes (A/C & furnace);wash clothes on “warm,” not “hot”1. Reduce consumption of fossil fuels.At home:bike instead of drive;carpool; energy-efficient vehiclesOn the road:2. Support environmental organizations.3. Rely on alternate energy sources.solar, wind energy,hydroelectric power
11 The Kinetic Molecular Theory (KMT) --explains why gases behave as they do-- deals w/“ideal” gas particles…1. …are so small that they areassumed to have zero volume2. …are in constant, straight-line motion3. …experience elastic collisions in whichno energy is lost4. …have no attractive or repulsive forces towardeach other…have an average kinetic energy (KE) that isproportional to the absolute temp. of gas(i.e., Kelvin temp.)as Temp. , KE
13 Theory “works,” except at high pressures and low temps. (attractive forcesbecome significant)N2 can be pumped intotires to increase tire lifeKMT “works”liquid nitrogen (N2);the gas condenses intoa liquid at –196oCKMT starts to break downliquidN2H2Ofreezesbodytemp.H2Oboils–196oC0oC37oC100oC
15 Model Gas Behavior All collisions must be elastic Take one step per beat of the metronomeContainerClass stands outside tape boxHigher temperatureFaster beats of metronomeDecreased volumeDivide box in halfMore MolesMore students are inside boxMark area of container with tape on ground.Add only a few molecules of inert gasIncrease temperatureDecrease volumeAdd more gasEffect of diffusionEffect of effusion (opening size)
16 Two gases w/same # of particles and at same **Two gases w/same # of particles and at sametemp. and pressure have the same kinetic energy.KE is related to mass and velocity: KE = ½ m v2KE1= ½m1v1sametemp.sameKE2KE2= ½m2v22To keep same KE, as m , v mustOR as m , v must .More massive gas particlesare _______ thanless massive gasparticles (on average).slower
17 Particle-Velocity Distribution (different gases, same T and P) N2 H2(2 g/mol)Particle-Velocity Distribution(different gases, same T and P)N2(28 g/mol)CO2(44 g/mol)CO2particles# ofN2H2(SLOW)Velocity ofparticles (m/s)(FAST)
18 Particle-Velocity Distribution (same gas, same P, different T) 10oCParticle-Velocity Distribution(same gas, same P, different T)50oC100oC10oCparticles# of50oC100oC(SLOW)Velocity ofparticles (m/s)(FAST)
19 ** To use Graham’s Law, both gases Consider two gases at same temp.Gas 1: KE1 = ½ m1 v12Gas 2: KE2 = ½ m2 v22Since temp. is same, then…KE1 = KE2½ m1 v12 = ½ m2 v22m1 v12 = m2 v22Divide both sides by m1 v22…Take sq. rt. of both sides to get Graham’s Law:** To use Graham’s Law, both gasesmust be at same temp.
20 For gases, rates of diffusion & effusion obey Graham’s law: particle movementfrom high tolow conc. (perfume)diffusion of gasparticles throughan opening (balloon)NET MOVEMENTNET MOVEMENTFor gases, rates of diffusion& effusion obey Graham’s law:more massive = slow;less massive = fast
21 On avg., carbon dioxide travels at 410 m/s at 25oC. CO2On avg., carbon dioxide travels at 410 m/s at 25oC.Find avg. speed of chlorine at 25oC.irrelevant, solong as theyare the sameCl2use molar masses= 320 m/s**Hint: Put whatever you’re lookingfor in the numerator.(the algebrais easier)
22 He Ne Ar Kr Xe Rn F2 mm = 38 g/mol 4.003Ne1020.180Ar1839.948Kr3683.80Xe54131.29Rn86(222)At a certain temp., fluorine gas travels at582 m/s and a noble gas travels at394 m/s. What is the noble gas?= g/molbest guess = Kr
23 CH4 moves 1.58 times faster than which noble gas? mm = 16 g/molHe24.003Ne1020.180Ar1839.948Kr3683.80Xe54131.29Rn86(222)Ne2or Ar?= g/mol“Ar?”Ar“Aahhrrrr! Buckets o’ blood!Swab de decks, ye scurvy dogs!”
24 A HCl and NH3 are released at same time from opposite ends of 1.20 m horiz. tube.Where do gases meet?HClNH3ABCmm = 36.5 g/molmm = 17 g/molmore massiveless massivetravels slowertravels fasterA
25 A P Gas Pressure Pressure occurs when a force is dispersed over a given surface area.If F acts over a large area…F=(e.g., your weight)PABut if F acts over a small area…PF=A
26 At sea level, air pressure is standard pressure: 1 atm = kPa = 760 mm Hg = 14.7 lb/in2Find force of air pressureacting on a baseballfield tarp…100 ft.2A = 10,000 ft.ftA = 10,000 ft2= 1.44 x 106 in2F = P A= lb/in2 (1.44 x 106 in2)= 2 x 107 lb.F = 2 x 107 lb.= 10,000 tonsKey:Gases exert pressurein all directions.
27 Atmospheric pressure changes with altitude: As altitude , pressure .barometer:device to measureair pressureVacuum(nothing)airpressuremercury (Hg)
28 Pressure and Temperature STP (Standard Temperature and Pressure)standard temperature standard pressure0oC273 K1 atm101.3 kPa760 mm HgEquations / Conversion Factors:K = oC + 2731 atm = kPa = 760 mm Hg
29 K = oC + 2731 atm = kPa = 760 mm HgConvert 25oC to Kelvin.K = oC + 273== KHow many kPa is 1.37 atm?1.37 atm101.3 kPa= kPa1 atmHow many mm Hg is kPa?231.5 kPa760 mm Hg= mm Hg101.3 kPa
30 Bernoulli’s Principle For a fluid traveling // to a surface:--FAST-moving fluidsexert ______ pressureLOWLIQUIDOR GAS--SLOW-moving fluidsexert ______ pressureHIGHLOW PFASTNETFORCEHIGH PSLOW
31 roof in hurricane or tornado… FASTLOW PSLOWHIGH P
32 airplane wing / helicopter propeller FASTResulting ForcesLOW P(BERNOULLI’SPRINCIPLE)AIRPARTICLESSLOWHIGH P(GRAVITY)frisbeeFAST, LOW PSLOW, HIGH P
33 creeping shower curtain COLDWARMSLOWFASTHIGH PLOW P
34 windows and high winds TALL BUILDING FAST LOW P SLOW windows burst outwardsHIGH P
35 manometer: measures the pressure of a confined gas AIRPRESSUREHg HEIGHTDIFFERENCEmanometer:measures the pressureof a confined gasCONFINEDGASSMALL + HEIGHT = BIGdifferentialmanometermanometers can be filledwith any of various liquids
36 Atmospheric pressure is 96.5 kPa; mercury height difference is233 mm. Find confined gaspressure, in atm.SX atm96.5 kPa233 mm HgBSMALL + HEIGHT = BIG96.5 kPa+233 mm Hg=X atmatm+atm=1.259 atm
37 Manometers HW #1 X atm SMALL + HEIGHT = BIG 125.6 kPa 0 mm Hg If H = 0, then S = B126 kPa = X atm126 kPa1 atm= atm101.3 kPa
38 Manometers HW #2 112.8 kPa B SMALL + HEIGHT = BIG S 0.78 atm X mm Hg 0.78 atm + X mm Hg = kPaConvert units into mm Hg…0.78 atm760 mm Hg= mm Hg1 atm112.8 kPa760 mm Hg= mm Hg101.3 kPa592.9 mm Hg + X mm Hg = mm HgX = mm Hg
39 The Ideal Gas Law P V = n R T P = pres. (in kPa) T = temp. (in K) V = vol. (in L or dm3)n = # of moles of gas (mol)R = universal gas constant = L∙kPa/mol∙K32 g oxygen at 0oC is under kPa of pressure.Find sample’s volume.T = 0oC = 273 KP V = n R TP= L
40 0.25 g carbon dioxide fills a 350 mL container at 127oC. Find pressure in mm Hg.T = 127oC = 400 KP V = n R TVV = 350 mL/1000 = L= 54.0kPa54.0 kPa= mm Hg
41 P, V, T Relationships At constant P, as gas T , its V ___ . balloon placed in liquid nitrogen(T decreases from 20oC to –200oC)
42 KABLOOEY! P, V, T Relationships (cont.) At constant V, as gas T , its P ___ .At constant V, as gas T , its P ___ .KABLOOEY!blown-out truck tire
43 P, V, T Relationships (cont.) At constant T, as P on gas , its V ___ .At constant T, as P on gas , its V ___ .Gases behave a bit like jacks-in-the-box (or little-brothers-in-the-box)
44 Derivation of the Combined Gas Law Consider a sample of gas under the conditions ofP1, V1, and T1.P1 V1 = n R T1(A)Now, change the gas sample’s conditions toP2, V2, and T2.P2 V2 = n R T2(B)But n and R are the same for both (A) and (B).Solve each equation for the quantity n x R.P1 V1T1=P2 V2T2This is thecombined gas law.n R =
45 The Combined Gas Law P = pres. (any unit) 1 = initial conditions V = vol. (any unit) 2 = final conditionsT = temp. (K)A gas has vol. 4.2 L at 110 kPa. If temp. is constant,find pres. of gas when vol. changes to 11.3 L.P1V1 = P2V2110(4.2) = P2(11.3)11.3P2 = 40.9kPa
46 423 KOriginal temp. and vol. of gas are 150oCand 300 dm3. Final vol. is 100 dm3.Find final temp. in oC, assumingconstant pressure.300(T2) = 423(100)300T2 = 141KT2 = –132oC
47 A sample of methane occupies 126 cm3 at –75oC and 985 mm Hg. Find its vol. at STP.198 KResearchers at U of AK, Fairbanks, saymethane has surfaced in the Arctic due toglobal warming. This methane couldaccount for up to 87% of the observedspike in atmospheric methane.985(126)(273) = 198(760)(V2)198(760)V2 = 225cm3
48 ( ) ( ) ( ) ( ) ( ) ( ) Derivation of the Density of Gases Equation Consider a sample of gas under two sets of conditions.P1 V1 = n R T1P2 V2 = n R T2P1 V1 = R T1massmm( )P2 V2 = R T2massmm( )D1D2( )P1 = T1massV1( )Rmm( )( )P2 = T2massV2RmmSolve each of these for the ratio R/mm...P1T1D1=P2T2D2=RmmDensity of GasesEquation
49 Density of Gases Density formula for any substance: For a sample of gas, mass is constant, but pres.and/or temp. changes cause gas’s vol. to change.Thus, its density will change, too.ORIG. VOL.NEW VOL.ORIG. VOL.NEW VOL.If V (due to P or T ),then… DIf V (due to P or T ),then… D
50 Density of GasesEquation:** As always,T’s must be in K.A sample of gas has density g/cm3 at –18oCand 812 mm Hg. Find density at 113oCand 548 mm Hg.386 K255 K812548=255(0.0021)386(D2)812(386)(D2) = 255(0.0021)(548)812(386)812(386)D2 = 9.4 x 10–4 g/cm3
51 A gas has density 0.87 g/L at 30oC and 131.2 kPa. Find density at STP.303 K131.2101.3=303(0.87)273(D2)131.2(273)(D2) = 303(0.87)(101.3)131.2(273)131.2(273)D2 = 0.75 g/LFind density of argon at STP.
52 Find density of nitrogen dioxide at 75oC and 0.805 atm. NO2348 KD of STP…10.805=273(2.05)348(D2)NO2 participates in reactionsthat result in smog (mostly O3)1(348)(D2) = 273(2.05)(0.805)1(348)1(348)D2 = 1.29 g/L
53 A gas has mass 154 g and density 1.25 g/L at 53oC and 0.85 atm. What vol. doessample occupy at STP?326 KFind STP…0.851=326(1.25)273(D2)0.85(273)(D2) = 326(1.25)(1)D2 = g/L0.85(273)0.85(273)Find vol. when gas has that density.= L
54 Dalton’s Law of Partial Pressure John Dalton (1766–1844)In a gaseous mixture, a gas’spartial pressure is the onethe gas would exert if it wereby itself in the container.The mole ratio in a mixture ofgases determines each gas’spartial pressure.Since air is ~80% N2, (i.e., 8 out of every 10 air-gas moles isa mole of N2), then the partial pressure of N2 accounts for ~80%of the total air pressure.At sea level, where P ~100 kPa, N2 accounts for ~80 kPa.
55 Total pressure of mixture (3.0 mol He and 4.0 mol Ne) is 97.4 kPa. Find partial pressure of each gas.= kPa= kPaDalton’s Law: the total pressure exerted by a mixtureof gases is the sum of all the partial pressuresPTot = PA2 + PB2 + …
56 80.0 g each of He, Ne, and Ar are in a container. The total pressure is 780 mm Hg. Find each gas’spartial pressure.PHe = 20/26of total80 g He= 20 mol HeTotal:26 molPNe = 4/26of total80 g Ne= 4 mol NePAr = 2/26of total80 g Ar= 2 mol ArPHe = 600 mm HgPNe = 120 mm HgPAr = 60 mm HgTotal pressure is 780 mm Hg
57 TOTAL PRESSURE (Ptot) IN LAST CONTAINER Two 1.0 L containers, A and B, contain gases under2.0 and 4.0 atm, respectively. Both gases are forcedinto Container Z (w/vol. 2.0 L). Find total pres. ofmixture in Z.ABZ1.0 L1.0 L2.0 L2.0 atm4.0 atmPRESSURESIN ORIG.CONTAINERSVOLUMESOF ORIG.CONTAINERSVOLUMEOF FINALCONTAINERPARTIALPRESSURES INFINAL CONTAINERP1V1V2P2AB=2.0 atm1.0 L1.0 atm2.0 L4.0 atm1.0 L2.0 atm3.0 atmTOTAL PRESSURE (Ptot) IN LAST CONTAINER
58 Find total pressure (PTot)of mixture in Z. BZC1.3 L L L L3.2 atm 1.4 atm atm X atmP1V1V2P2ABC=3.2 atm1.3 L1.81 atm1.4 atm2.6 L2.3 L1.58 atm2.7 atm3.8 L4.46 atm7.85 atm
59 Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g) Gas StoichiometryFind vol. hydrogen gas made when 38.2 g zinc reactw/excess hydrochloric acid. Pres.=107.3 kPa;temp.= 88oC.Zn (s) HCl (aq) ZnCl2 (aq) + H2 (g)38.2 g Zn excess V = X L H2P = kPaT = 88oCNot at STP!ZnH2361 K38.2 g Zn= mol H2P V = n R T= L
60 What mass solid magnesium is req’d to react w/250 mL carbon dioxide at 1.5 atm and 77oC to produce solidmagnesium oxide and solid carbon?2 Mg (s) + CO2 (g) 2 MgO (s) + C (s)X g Mg V = 250 mL0.25 LP = 1.5 atmkPaT = 77oC350 KCO2MgP V = n R T= mol CO20.013 mol CO2= g Mg
61 Vapor Pressure -- a measure of the tendency for liquid particles to enter gas phase at a given temp.-- a measure of “stickiness” of liquid particlesto each othermore“sticky”less likely tovaporizeIn general:LOW v.p.not very“sticky”more likely tovaporizeIn general:HIGH v.p.
62 A liquid’s VP depends on the temp. AND what substance it is. 100CHLOROFORM80PRESSURE(kPa)60ETHANOL40WATER2020406080100TEMPERATURE (oC)_______ substances evaporate easily(have high v.p.’s).VolatileBOILING vapor pressure = confining pressure(usually fromatmosphere)
63 At sea level and 20oC… NET NET PRESSURE PRESSURE (~95 kPa) (~90 kPa) AIR PRESSURE(~100 kPa)V. P.(~10 kPa)VAPORPRES.(~5 kPa)ETHANOLWATER
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