H2 Chemistry Explanations

Atomicstructure● StatethedefinitionofatomicmassItistheratiooftheaveragemassofoneatomofanelementto1/12themassofone 12 Catom ● StatethedefinitionofisotopicmassItistheratioofthemassofoneatomofanisotopeofanelementto1/12themassofone 12 Catom ● GiveninformationabouttheN–ObondinNO3 - whyisitinaccuratetorepresentNO3 - ashavingdoubleandsinglebonds?N–OisoflengththatisintermediatebetweentheoreticalN–OandN=Obondlength,soinaccurate. ● SuggestthemixingandoverlapofatomicorbitalswhichaccountforthepartialdoublebondcharacterinN-Obond.1. Mixing2. Overlap3. Explainhowresonancearisesa. Continuousside-wayoverlap→pielectronsdelocalize→givesrisetoresonancestructure→partialdoublebondcharacter ● ExplainifthemoleculeNCCNispolarC—Nbondispolardipolemomentscanceleachotherbecauseatomsarearrangedlinearlynonetdipolemoment ● Howdoesid-idandpd-pdariseElectronsinelectroncloudmoverandomly→unevendistributionofelectroncloud→instantaneousdipole→inducedipoleinadjacentmolecule ● Bondangleingraphene(planar)is120 0 . ● WhyisSrdenserthanCaIncreaseinmassismoresignificantthanincreasedsizeofSr.Noneedtobringinstrengthofmetallicbonding. Redox● Ag2O+H2O2->2Ag+O2+H2O.ExplainwhyH2O2actsasRA.Oxygenappears2timesonthereactantside(disproportionation),sodon’tfocusono.s.OfO.Focusonotherreactant(Ag). Physical periodicity● ExplainwhysuccessiveI.E.increasesgenerally.[2m] 1) Numberofprotonsconstant,numberofelectronsdecreasing.2) Nuclearattractionincreases 1

● (Givendata)Stateandexplainthegroupnumberofelementxx.[2m] 1) ThereisalargespikefromwhichI.E.towhichI.E.2) TheXXthelectronisremovedfromtheinnerprincipalquantumshell/Therearexxvalenceelectrons ● CalculateenergyneededtoremovexxxmolesofelectronsTotalenergy=ionisationenergy*amtofelectronsCuzionisationenergyisenergyfor1moleofelectrons ● WhyionicradiiofarandomionandaTMionaresimilarTMion:highernuclearcharge,greatershieldingeffect,furtherawayfromnucleus.Butnuclearattractionissimilarcuz3delectronsprovidepoorshielding Chemical Bonding● Explaintheshapeofxxx. 1) Statenumberoflonepairsandbondpairs.2) ByVSEPRtheory,electronpairsareplacedasfarapartaspossibletominimisemutualrepulsion. ● Suggestabondangleofxxx. 1) Statenumberofloneandbondpairs.2) xxrepulsionislargerthanxxrepulsion(lplp>lpbp>bpbp)3) IfqnsayuseVSEPRtheory,statethatbyVSEPR,electronsareplacedasfarapartaspossibletominimiseinterelectronicrepulsion VSEPR:includesboth2and3 ● WhyisC–Cbondbtwsp2-sp3orbitalsstrongerthanbtwsp3-sp3orbitals Btwsp2-sp3:Covalentbondhashigher%ofscharacterMoreeffectiveorbitaloverlap Content:● CCl4andSiCl4aresimplemolecules!● strengthofcovalentbond:○ Bondorder:i. #oforbitalsoverlappedii. electrondensitybetweenbondingatomsiii. attractionbetweenbondingnucleiandsharedelectrons○ Effectivenessoforbitaloverlap:i. %ofscharacter inhybridorbital● “sp2-sp2overlapinXismoreeffectivethansp3-sp3overlapinYduetohigher%ofscharacterinhybridorbitals.” 2

ii. atomicsize ● WhycanAlCl3formdativebondstobecomeadimerAlatomhasemptyorbital,canacceptlonepairelectronsfromCl ● IntramolecularHbondOnlypossibleiftheringhasmorethan5atoms.Ifless,thereisringstrain,notpossible.Keywords:XXXformsintramolecularHbondingwhichreducesthenumberofsitesavailableforintermolecularHbonding. ● IntramolecularHbond→conjugatebaseofcisisomerismorestablethantransisomer→cisisomerismoreacidicPastmistake:lessextensiveHbond→lessacidic(illogic!) ● Atthestart,definestructureandbonding○ X,YandZhavesimplecovalentmolecularstructurewithweakintermolecularforcesofattraction.● Aminoacids:existaszwitterions,notgiantioniclatticestructures.● Hbond:○ Sameextensiveness→Seepolarity.■ O–HbondismorepolarthanN–Hbond.Moreenergy…strongerHbond.● ExplainwhyKClisnotvolatile○ Exactlythesameaswhyithasahighboilingpoint.(Structure:ioniclattice+Bonding:ionic+largeamtofenergyneededtoovercomeduringboiling→thusnonvolatile) ● ExplainthedifferenceinsolubilityofXandY○ Iftheyhavesamebondtype,comparebondstrength● VSExplainthedifferenceinsolubilityofXandYinsolvent○ MorefavourableinteractionsareformedbetweenXandsolvent● VSExplainwhyXdissolvesinsolvent○ EnergyreleasedfromformationofinteractionsbetweensolventandXissufficienttoprovideforenergyrequiredtoovercomeFOAbetweenXmolecules ● Whycangrapheneconductelectricity○ (eachsp2hybridisedcarbonformscovalentbondswith3othercarbonatoms)○ continuouslateraloverlapofunhybridizedporbitals○ pelectronscandelocalisetoconductelectricity ● Ioniccompoundscharacteristics:○ Hardandbrittle○ Conductelectricityinmoltenstate,notinsolidstate○ Highmelting,boilingpoint● Id-id○ GreaterMr/surfacearea->greaterelectroncloudsize->dipolesaremoreeasilyinduced ● Whytransisomerismorestablethanthecisisomer○ Lesssterichindrance 3

Gaseousstate ● Statethe3assumptionsofthekinetictheoryasappliedtoidealgases1) Gasparticleshavenegligiblevolumeascomparedtothevolumeofcontainer2) IntermolecularFOAbtwparticlesandbtwparticlesandwallsarenegligible3) Collisionsbtwparticlesareperfectlyelastic(notimportant) ● ExplainwhyexperimentalvalueofamountishigherthantheoreticalvalueBreakassumption2:non-negligibleFOAcuzthereissignificant idid(or pdpd, dependingonthemolecule)interactionsbetweenparticles→pressureislower ● Explaintheconditionsneededforrealgastobehavemorelikeidealgas.- LowpressureVolumeofparticlesbecomesmallerrelativetovolumeofcontainerGasparticlesfurtherapartfromoneanotherExperiencelessintermolecularFOA- HightempGreaterKE,overcomeintermolecularFOA ● Ifagashasmoredeviationatlowpressure,itshouldhavemoredeviationathighpressuretoo. ● Assumptions:(whenqnaskswhypressureisdifferentfromcalculatedpressure)○ Idealgas○ Thereareothergasesthatcontributetototalpressure■ Qnhas1vesselwithonlyO2gas,anothervesselwithO2andwater.The2ndvesselisassumedtoonlyhaveO2,butmayhavewatervaporthatcontributestototalpressure.● UNITSOFVOLUMEINPV=NRTMUSTBEMETERCUBED. Kinetics● Explainwhyreactiondoesnotoccurinthelaboratorybuttakesplacereadilyin____. 4

- Whynotinlab:Highactivationenergy- Whycaninsomewhereelse:havecatalysttoloweractivationenergy ● givenconc-timegraph,provereactioniszeroorderwrtreagent- straightlinegraph- rateisindepof[?] ● given2conc-timegraphs,proverxnis1storder- calculategradientsandshowworkinginanswer ● Whyisthisreactionunlikelytohappen?ActivationenergytoohighORlookatnumberofreactants→ifmanyreactantspecies→unlikelyforXreactantstocollideatsametimeforsuccessfulcollision ● WhyisrateofreactionbetweenS2O8 2- andI - slow/whyisreactionobservedtonotoccurNegativelycharged→highactivationenergy→fewparticleshavehighenoughenergyforreactiontoproceed→slowrxn(examskill:ifpreviouspartalrasktoshowthatreactioncanpossiblyoccur,gibbsfreeenergy,thennextpartshouldberegardingrate/kinetics) Content:rate=k[?]→Sn1unimolecularrate=k[?][?]→Sn2bimolecular ● ExplainwhyHCldoesn’treactwithalkenesviafreeradicaladditionunlikeHBr.Quotebondenergies→H-Clbondisstronger→higher activationenergy(link)→rxndoesnotoccur ● WhyislargeexcessofAadded[A]isconstant.[A]doesnotaffectrate. ● Howdidsecondorderreactionbecomefirst-orderAtfirstrate=k[A][B]Aisinexcess,[A]isconstant,reactionbecomespseudofirst-orderreaction ● Continuingaboveqn:outlinesuitableexperimenttodeterminevaluefork.Continuousmethod:addexcessASampling:addreactantstgt.atsuitabletimeintervals,extractanaliquotusingapipette.Quenching:addalargevolumeoficecoldwatertotherxnmixturetoquenchit.Titration:titrationwithNaOH,plotgraphofVNaOHagainsttime,findhalflife.k=ln2/halflife ● Howdoesheterogeneouscatalystwork1. Rxtsadsorbontoactivesitesofcatalyst.Weakinteractionsformbetweencatalystandrxts2. Oncatalysta. Catalystbringsrxtsclosetogetherb. Interatomic/intramolecularbondsinrxtsareweakened.Rxtmoleculesarebroughtclosertogether.c. Activationenergyislowered 5

3. Rxtsdesorbfromcatalyst,regeneratingcatalyst ● Giventhatrate=k[A],explainwhichstepistherate-determiningstep.1. A→B+C2. B+C→B+D+E3. A+D→BStep1istheratedeterminingstep.Thereactionis1storderwrtA,sotheratedeterminingstepcanonlyhave1A. ● Iftheexperimentwasrepeatedatthesameconditionbut[reactant]isdoubled,howdoesthevalueofrateconstantchange?Rateconstantisonlydependentontemperatureandcatalyst,soitisunchanged. ● Inanenzyme-catalysedreaction,howdoesratevarywith