Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high...

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Section 8: Gases The following maps the videos in this section to the Texas Essential Knowledge and Skills for Science TAC §112.35(c). 8.01 Simple Gas Laws • Chemistry (9)(A) 8.02 Ideal Gas Law • Chemistry (9)(A) 8.03 Partial Pressure • Chemistry (9)(A) 8.04 Application of the Ideal Gas Law • Chemistry (9)(B) 8.05 Graham’s Law of Effusion • N/A 8.06 Kinetic Molecular Theory • Chemistry (9)(C) Note: Unless stated otherwise, any sample data is fictitious and used solely for the purpose of instruction. Safety Note: Any chemicals mentioned in these videos are potentially harmful and should be handled with the appropriate safety precautions. Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 1

Transcript of Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high...

Page 1: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

Section8:GasesThefollowingmapsthevideosinthissectiontotheTexasEssentialKnowledgeandSkillsforScienceTAC§112.35(c).8.01SimpleGasLaws

• Chemistry(9)(A)8.02IdealGasLaw

• Chemistry(9)(A)8.03PartialPressure

• Chemistry(9)(A)8.04ApplicationoftheIdealGasLaw

• Chemistry(9)(B)8.05Graham’sLawofEffusion

• N/A8.06KineticMolecularTheory

• Chemistry(9)(C)Note:Unlessstatedotherwise,anysampledataisfictitiousandusedsolelyforthepurposeofinstruction.

SafetyNote:Anychemicalsmentionedinthesevideosarepotentiallyharmfulandshouldbehandledwiththeappropriatesafetyprecautions.

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Page 2: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

8.01

SimpleGasLaws

Thepressureofagasisdefinedastheforcethatthegas’sparticlesexertonthewallsofacontainerperunitarea.Recallthatagasisreadilycompressiblebecauseofthelargeamountofemptyspacebetweenparticles.

Abarometerisadevicecommonlyusedtomeasureatmosphericpressure.Whenalongtubeisfilledwithmercuryandturnedupsidedownonadishalsofilledwithmercury,theheightofthemercuryinthetubeshowstheatmosphericpressureoutside.TheSIunitforpressureisthepascal(Pa),aderivedunitthatisdefinedasonenewtonpersquaremeter.Therearemanyothercommonunitsofpressure,showninthetablebelow.

SIUnitofPressure CommonEquivalentUnits

101.325kilopascals 1atmosphere 1.01325bar 760mmHg 760torr 14.7psi

1. In1980,HurricaneAllenmadelandfalloverBrownsville,Texas.Withsustainedwindsover190mph,itstillstandsasoneofthestrongesthurricaneseverrecorded.AtthepeakofHurricaneAllen’sstrength,thepressureneartheeyewasmeasuredas899millibars(Roth,n.d.).Convertthispressureintokilopascalsandatmospheres.

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Page 3: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

Thepressureofagascanbeaffectedbythreefactors:• Theamount(n)ofagaspresentinacontainer,usuallyexpressedinunitsofmoles

• Theabsolutetemperature(T)ofthegas,inunitsofkelvin

• Thevolume(V)thatthegasoccupies,expressedinmanydifferentunits,mostcommonlyliters

ToconvertfromdegreesCelsiustokelvin,usetheformula

! = °% + 273.15

Thelawsthatdescribetherelationshipsamongthesevariablesholdstruewhenweassumethegasisbehavingideally,whichisavalidassumptionatconditionsofrelativelylowexternalpressureandrelativelyhightemperatures.Wemustalsoassumethatthepropertiesdiscusseddonotdependontheidentityofthegas.

• Boyle’slawstatesthatforagivenamountofgasataconstanttemperature,thepressureandvolumeofthegasareinverselyproportionaltoeachother.

-./. = -0/0

• Charles’slawstatesthatforagivenamountofgasataconstantpressure,thevolumeofthegasisdirectlyproportionaltothetemperatureofthatgas.

/.1.= /010

• Gay-Lussac’slawstatesthatforagivenamountofgasataconstantvolume,the

pressureofthegasisdirectlyproportionaltothetemperatureofthatgas.-.1.= -010

• Thecombinedgaslaworgeneralgaslawstatesthatforagivenamountofgasata

constantvolume,therelationshipamongpressure,volume,andtemperaturecanbeexpressedasshownbelow.

-./.1.

= -0/010

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Page 4: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

2. Inalaboratoryexperiment,arigid5.0-litercylinderisfilledwithamassofheliumgas.Atatemperatureof27°C,thegasexertsapressureof450torronthewallsofthecylinder.Thesafetyinformationfortheprocedurestatesthatthecylinderwillruptureiftheinternalpressureexceeds1,000torr.Whatisthemaximumtemperaturetowhichthecylindercanbeheatedbeforeitruptures?

A. 667°C B. 394°CC. 122°C D. 54°C

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Page 5: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

8.02

IdealGasLaw

Theidealgaslawexpressestherelationshipofthepressure(P),volume(V),temperature(T),andamount(n)ofagas,andtheidealgasconstant(R).

PV=nRTTheidealgasconstanthasavalueof0.0821(atm·L)/(mol·K).TomaintainunitconsistencywiththevalueofR,thepressureofthegasmustbeexpressedinatmospheres,thevolumeexpressedinliters,theamountexpressedinmoles,andthetemperatureexpressedinkelvin.

1. Whatmassofneongasiscontainedina2.50-literballoonat50°Cand400.0mmHg?

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Page 6: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

2. Analternativeformofthegasconstant,R,hasthevalue8.314(kPa·L)/(mol·K).Usethisconstanttofindthetemperaturetowhicha25-gramsampleofoxygengasmustbeheatedinorderforittoreachapressureof150.0mmHgifthegasoccupiesaconstantvolumeof375milliliters.

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Page 7: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

8.03

PartialPressure

Inamixtureofgases,theindividualpressurecontributionofeachgasisreferredtoasthepartialpressureofthatgas.Thepartialpressureofagasisdirectlyproportionaltothemolefractionofthespecifiedgasinthemixture.

P3 = χ3 · P6789:

Themolefractionofagasinamixturecanbecalculatedastheratioofthemolesofthespecifiedgastothetotalmolesofgaspresentinthemixture.

χ3 = molesofAtotalmoles

Forexample,consideramixtureofonemoleofneongasandfourmolesofxenongas,exertingatotalpressureof25.0kPa.

Dalton’slawofpartialpressuresstatesthatthetotalpressureofamixtureofgasesisthesumoftheindividualpartialpressuresofthegasesinthesystem.

P6789: = P3 +PD +PE …

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Page 8: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

1. Agasmixtureconsistsofequalmassesofcarbondioxideandneon.Ifthepartialpressureoftheneonis300mmHg,whatisthepartialpressureofthecarbondioxide?

A. 438mmHgB. 405mmHgC. 138mmHgD. 216mmHg

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Page 9: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

8.04

ApplicationsoftheIdealGasLaw

Theidealgaslawallowsustorelatetheamountofagaspresenttothepressure,temperature,andvolumeofthegas.Thus,wecanusetheidealgaslawtoperformstoichiometriccalculations.

1. Solidmagnesiumreactswithoxygengasaccordingtothereactionbelow.

2Mg(s)+O2(g)®2MgO(s)

Whatvolumeofoxygengas,at300kelvinand855millibars,willfullyreactwith25gramsofmagnesium?1atm=1013.25millibars

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Page 10: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

2. Inaprocesscalledelectrolysis,anelectriccurrentpassedthroughwatercauseshydrogengasandoxygengastobeevolved.Theunbalancedreactionbelowshowsthisprocess.

H2O(l)®H2(g)+O2(g)

Ifa12.5mLsampleofwateriselectrolyzeduntilalltheliquidwaterisgone,whatvolumeofoxygengasisproducedat100°Cand1atm?

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Page 11: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

8.05

Graham’sLawofEffusion

Effusionistheprocessbywhichagasescapesfromasmallholeinacontainer.Graham’slawofeffusionstatesthattherateofeffusionofagasisinverselyproportionaltothesquarerootofitsmolarmass.

RateofEffusionofGasARateofEffusionofGasB

= molarmassofGasBmolarmassofGasA

Thegreaterthemolarmassofagas,the___________itseffusionrate,and

the___________timeittakesforthegastoeffuse.

1. Aballoonisfilledwithequimolaramountsofxenongas,oxygengas,andheliumgas.After24hours,theballoonisnoticeablysmallerinsize.Basedonrelativeratesofeffusion,rankthegasesfromlargesttosmallestintermsofpartialpressureafter24hours.

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Page 12: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

2. Ifanunknowngaseffusesthroughaholeinacontainer1.87timesfasterthanchlorinegas,whichofthefollowingisclosesttothemolarmassoftheunknowngas?

A. 17.64g/molB. 32.07g/molC. 20.28g/molD. 247.9g/mol

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Page 13: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

8.06

KineticMolecularTheory

Thekineticmoleculartheoryofgasesdescribesthebehaviorofidealgasesattheatomiclevel.Thetheoryhasthreeimportantpostulates:

• Gasesconsistofparticleswhoseseparationismuchgreaterthanthesizeoftheparticlesthemselves.

• Theparticlesofagasareinconstantmotion.Themovementofthegasescauseselasticcollisionswithothergasparticlesandthewallsofthecontainer,buttheparticlesdonotloseenergy.

• Theaveragekineticenergyofagasdependsonlyonthetemperatureofthegas.

!OPQR = 12ST0 =

32U1

Innormalconditions(relativelyhightemperaturesandlowexternalpressure),mostgasesexhibitnearlyidealbehavior.However,thepostulatesofthekineticmoleculartheoryfailtoexplainthebehaviorofrealgasesatlowtemperaturesorhighexternalpressures.Forarealgas,thePV/RTratiocanbeplottedagainstexternalpressure(Pext)toshowhowincreasingtheexternalpressurecausesnon-idealbehavior.Atmoderatelyhighpressure,thevalueofPV/RTislessthan1,duepredominantlytoforcesofattractionamongthegasparticles.Atveryhighpressure,thevalueofPV/RTisgreaterthan1,duepredominantlytothemolecularvolumeofthegasparticles.

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Page 14: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

1. Considertwoseparate,evacuatedone-litercontainersat35°C.OnegramofO2gasisplacedintooneofthecontainersandonegramofCl2gasisplacedintheothercontainer.Whichofthefollowingstatementswillbetrue?

A. TheCl2gaswillexhibitahigherpressure.B. TheO2gaswillhaveahigherdensity.C. TheCl2gaswillhavefewermolecules.D. Atveryhighpressures,theratioofPVtoRTwillbegreaterthan1fortheO2gasbecause

offorcesofattraction.

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Page 15: Section 8: Gases - Study Edge · explain the behavior of real gases at low temperatures or high external pressures. For a real gas, the PV/RT ratio can be plotted against external

References

Roth,David.(n.d.).“HurricaneAllen-August1-14,1980.”Retrievedfromhttp://www.wpc.ncep.noaa.gov/tropical/rain/allen1980.html

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