SOR, energy change, redox

dohnotes Speedofreaction=howfastorhowslowareactionis-doanexperimenttomeasurechangeoveraperiodoftime(equations):-amtofreactantusedup/timetaken-amtofproductobtained/timetaken-volofgasproduced/timetaken Experimentnotes:H2isgivenoff:usegassyringe-H2isverylightandthechangeisminimalleadingtounreliableresultsCO2givenoff:masschange-CO2isaheaviergasCottonwool:allowgastoescapeandpreventsolutionfromsplashingGraphsofmass-doesnotreachzero Collisiontheory:-forareactiontotakeplace,theremustbeacollisionbetweenreactantparticles,someareunsuccessful.-asuccessfulcollisionisonewherethecollidingparticleshaveenoughenergytoreact(minimumactivationenergy) Catalyst(usuallytransitionmetals/oxides):=asubstancethatspeedsupachemicalreaction,withoutbeingusedupitself-changethespeedofreaction,nottheyieldofproductobtained-smallamounts→significanteffectsIndustryuse:reducefuelbillsifthereactionisfastenoughatlowertemperaturenote:catalystslowertheactivationenergyofareaction Factors:1.Particlesize-thesmallerthesize,thefasterthereaction-smallerparticlesize=largertotalsurfaceareaforcollisionoftheparticles=higherfrequencyofcollision=higherfrequencyofeffectivecollisionapplication:coaldustburnsfasterthanlargepiecesofcoal=powderedcoalisusedinmoderncoal-burningpowerstations-explosionscanoccuriftheaircontainstoomuchcoaldust(sparksfrommachinerycausesexplosion)=removedustbysprayingwater 2.Concentration-thehighertheconcentration,thefasterthereaction-higherconcentration=greaternumberofreactantparticlesinaunitvolume=higherfrequencyofcollision=higherfrequencyofeffectivecollision 3.Pressure-thehigherthepressure,thefasterthespeedofreaction-higherpressure=particlesareclosertogether=higherfrequencyofcollision=higherfrequencyofeffectivecollision 4.Temperature-thehigherthetemperature,thefasterthereaction-highertemperature=particlespossessmoreke=moveathigherspeedsandcollidewitheachotherwithgreaterforce=greaternumberofparticleswiththeminimumactivationenergy=higherfrequencyofcollision=higherfrequencyofeffectivecollision

dohnotes Heatofreaction(energychange)Enthalpychange:theamountofenergyabsorbedorreleasedinachemicalreactioncarriedoutunderconstantpressure Δ H=HEATABSORBEDDURINGBONDBREAKING-HEATRELEASEDDURINGBONDFORMING Exothermicreactions-givesoutheattothesurroundings(feelshot)Characteristics:-tempofsurroundingsincrease-productshavelessenergythanreactants-negativeΔ H(tempincreasesrapidlyafterthereactionbeginsasheatenergyisgivenofftotheenvironment,tempfallsgraduallyafterreactioniscompleteandreturnstoroomtemp)*thetotalamountofenergyabsorbedinbreakingthebondsinthereactantsisLESSTHANthetotalamountofenergyreleasedfrombondformingintheproducts Endothermicreactions-takesinheatfromsurroundings(feelscold)Characteristics:-tempofsurroundingsdecrease-productshavehigherenergythanreactants-positiveΔ H(tempdecreasesrapidlyafterthereactionbeginsasheatenergyistakeninfromtheenvironment,tempgraduallyincreasesafterreactioniscompleteandreturnstoroomtemp)*thetotalamountofenergyabsorbedinbreakingthebondsinthereactantsisMORETHANthetotalamountofenergyreleasedfrombondformingintheproducts Energyprofilediagram *catalystreducestheactivationenergyneeded Catalyst:speedsuptherateofreactionwhileremainingchemicallyunchangedattheendofthereaction Examples(exothermic)-Nuclearfission;largeatomicnucleus,suchasuranium,issplitinto2orsmallerparticles-Combustion;useofoxygentoburnfuel-Neutralisation;freemovingaqhydrogenandhydroxideionscometogetherandformbonds-Respiration;useofoxygentoburnglucoseC6H12O6+6O2->6CO2+6H2O+energy-Convertinganhydroussalttohydratedsalt;CuSO4+H2O->CuSO4.5H2O-Haberprocess;manufactureammonia-Contactprocess; 2SO2+O2->2SO3(physicalprocess)-condensation,freezing,dissolvingofanhydroussalt/acids Examples(endothermic)-Thermaldecompositionofcarbonateandnitratesalts-Dissolvingcrystalsofpotassiumorammoniumsaltsinwater-Photography;lightfallsonsilverbromideandagitateanelectroninBr-andcausesittomovetoAg+causingthecompoundtobreakupandformdarkareasonthefilm2AgBr(underlight)->Br2+2Ag(redox)-Photosynthesis;6CO2+6H2O->C6H12O6+6O2(physicalprocess)-evaporation,melting,dissolvingsomeioniccompounds

dohnotes Redoxreaction-areactionwherebothreductionandoxidationtakesplaceconcurrently O R + S - - H + + O - - E + S:oxidationstateH:hydrogenO:oxygenE:electrons Explanation: Oxidation-increaseinoxidationstate*-losehydrogen-gainoxygen-lossofelectrons Reduction-decreaseinoxidationstate*-gainhydrogen-loseoxygen-gaininelectrons *itis(oxidised/reduced)astheoxidationstateof__(increase/decrease)from(+/-)__in__to(+/-)__in__ Oxidisingagent(OA):asubstancethatcausesanothersubstancetobeoxidisedwhileitselfbeingreduced Reducingagent(RA):asubstancethatcausesanothersubstancetobereducedwhileitselfbeingoxidised OA Testfor RA RA TestforOA oxygen,ozone hydrogen halides*Iodinesolution Browntocolourless(I-ions)oxidizingpowerofhalogensdecreasesdownthegroup sulfurdioxide,hydrogensulfide copper(II)oxide** lowreactivemetal+O2(easilyloseO2toothercompounds) Carbon,CO AcidifiedKMnO4 Purpletocolourless metals*** reducingabilityof groupImetalsincreasesdownthegroup AcidifiedK2Cr2O7 Orangetogreen AcidifiedFeSO4 Greentoyellowororangeorbrown(Fe3+ions) FreshFeCl3 Yellowtogreen(Fe2+ions) AcidifiedKI Colourlesstobrown(I2aq) H2O2 ALSORA ConcHCl Cl2formed