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Standard answers:1 Basic concepts, Fuels, alkanes and alkenes:Effect of chain length on boiling point / volatilityAs chain length increases – boiling point increases / volatility decreasesMore electrons – greater VDW forces of attractionEffect of branching on the boiling point / volatility of the isomersMore branching decreases the boiling point / increases volatilitySame number of electrons but smaller surface areaDecreases VDW forces of attractionExplain how fractional distillation worksEach fraction has different boiling points due to different VDWTherefore condense at different temperaturesExplain the nature of the C = CExplain why E/Z or trans/cis isomerism occurs in some alkenesTran E - a cross dresser / a cross the C=CDouble bond does not allow rotationEach C atom of the double bond is bonded to 2 different groupsDealing with polymer waste:Sort and recycleFeedstock recyclingIncinerate (emits CO2)Biodegradable polymers2A Alcohols and halogenoalkanes:Explain why alcohols have higher Bpts / liquids instead of gasesHas HB which is stronger than VDWExplain the solubility of alcohols in waterHas HB like waterChain length decreases the efficiency of HBOxidation of alcoholsCH3CH2OH+[O]CH3CHO+H2ORate of hydrolysis of the halogenoalkanes (forming alcohols and halide ion)PolarityBond strengthReaction+ Ag+RateConclusion13CH3ClCH3OH + Cl-W ppt3Must be due to bond strength as that ppts 1st22CH3BrCH3OH + Br-C ppt231CH3ICH3OH + I-Y ppt1Possible application of knowledge - Rate of hydrolysis based on structure:Reaction+ Ag+RateConclusion1oCH3CH2CH2ICH3CH2CH2OH + I-Y ppt3Therefore 3o must have some reason – not in spec – about interpreting2o(CH3)2CH2I(CH3)2CH2OH + I-Y ppt23o(CH3)3I(CH3)3OH + I-Y ppt12B – Analysis% Yield = Actual amount (moles) x100 Theoretical amount (moles)Is a measure of the amount of conversionAtom economy = Mr of desired product x100 Sum of all Mr’s of all productsIs a measure of sustainabilityImproved by finding a use for undesired productsIR SpectroscopySpecific bonds absorb specific IR frequencies making the bonds vibrateThis frequency of IR is absorbed and shown as a peak on the spectraMass SpectroscopyIonisationAccelerationDeflection OR Time of flightDetectionMolecular IonM + e- M+ + 2e-The Mr of a molecule shown by the highest m/z valueFragmentsM+ F+ + FWhen the molecular ion fragments into a 2 smaller molecular fragments, only one with a (+)ve chargeEach molecule has its own unique mass spectra determined by its own fragmentation patterns3A – EnergyEnergy / enthalpy profile diagrams – ExothermicEnthalpy content of the reactants > enthalpy content of productsEnergy / enthalpy profile diagrams – EndothermicEnthalpy content of the products > enthalpy content of reactantsWhy does ?? reaction not happen?It has a high activation energyCalculating ?H – from temperature changesQ = mc?T (Kj) 1000REMEMBER m IS VOLUME OF LIQUID WITH THERMOMETER INMoles = mass = C x V(dm3) Mr REMEMBER TO USE LIMITING REAGENT?H = Q (Kj)?????????molesSIGN: ?T (-)ve???T (+)veMain sources of error in Enthalpy calculationHeat loss to the surroundings – insulateNot carried out under standard conditionsStandard conditions1atm pressure298k1 mole / molar solutionsNormal physical states under above conditionsExothermic reactions in terms of bond breakingMore heat energy is given out when new bonds forming the products than taken in to break the bonds of the reactantsEndothermic reactions in terms of bond breakingLess heat energy is given out when new bonds forming the products than taken in to break the bonds of the reactantsHess’ cyclesLOOK AT THE TABLE STUPID:Formation: arrows up / elements at the bottomCombustion: Arrows down / CO2 and H2O at the bottom (may be other oxides)Carbonates and acids: Arrows down / salt, CO2 and H2O at the bottomAny unfamiliar situation: Arrows likely to go down / products will be the same for each reactionsCHECK YOUR ROUTE AGAINST ARROWS AND CHAGE SIGN IF THEY ARE OPPOSITE3B - Rates:Collision theoryE > EaOrientation upon collisionHow an increase in concentration / pressure affects rateIncreases particles per volumeIncrease in collision frequencyIncreases rateHow an increase in pressure affects rateIncrease in pressure increases concentrationIncreases particles per volumeMore successful collisionsIncreases rateHow an increase in surface area increases rateSmall particle size increases surface areaMore area for collisionsIncreases rateHow catalyst increases rateProvides alternative route with a lower EaMore particles have E > new lower EaMore successful collisionsHow an increase in temperature increases rateTotal area under curve does not changeMore particles have E > Ea (shaded red)Increases collision frequencyMore successful collisionsIncreases rateCurve is lower and shifts to the rightFeatures on the Boltzman distributionArea = number of particlesNo particles can have zero energyNo maximum for a moleculeOnly E > Ea will react3B - EquilibriaFeatures of an equilibriumClosed systemDynamicWhat can be said about the forward and reverse reactions at equilibriumThe rate of the forward and reverse reactions are the sameEffect of pressure on equilibriumIncreasing P moves the eqm to the side with fewer moles of gas (and vice versa)Effect of temperature on equilibriumIncreasing temperature moves the eqm to the endothermic side (and vice versa)Effect of concentration on equilibriaIncreasing the concentration moves the eqm to the opposite side in order to remove (and vice versa)Discuss the conditions in the Haber process (or any other that they give)Always discuss rate, yield (equilibria) and cost (safety) ? N2(g)?? +?? 3H2(g)????? ?????? 2NH3(g)???????????? ?H = -92KjMol-1??????????????????? Endothermic?????????????Exothermic???????????????????4 high pressure??????????2 low pressure?ProcessEquilibriaRateCompromiseTemperatureDecrease temperature – will move equilibria to the exothermic side – the productsIncrease temperature – will increase the rate of reaction as activation energy is more likely to be overcome.Moderate temperature PressureIncrease pressure – Moves equilibrium to products with fewest moles of gas.Increase pressure – will increase the rate of reaction as more particles per volume.Cost of pumps and reaction vessel becomes very expensiveCatalystNo effect Increases the rate Finely divided iron Remove ammonia as it is formedRecycle unreacted H2 and N2??4 ResourcesWhat causes global warmingGreenhouse gases in the atmosphereAbsorb IR radiationEmit energy as heat3 Factors which affect global warmingAtmospheric concentrationAbility to absorb IRLife span in the atmosphereOutline 2 ways for C storageStored as a carbonate by reaction with CaO / MgOCaO + CO2 CaCO3Stored in disused oil wells under the sea bedWhy is the Ozone layer importantAbsorbs harmful UV raysHow does ozone absorb UVO3 + UV O2 + OO + O2 O3 + heatHow is ozone formedO radical reacts with O molecule forming ozoneO + O2 O3Then rate of formation of ozone = decompositionO + O2 ? O3How does catalytic converters workAdsorptionWeaker bonds allow reaction to occurDesorptionDiesel engine catalystsConvert CO to CO2Completely combust un burnt hydrocarbonsPetrol engine catalysts – as above plus:2NO + 2CO N2 + 2CO2Green chemistryIncrease atom economy (low = unsustainable) – find use for waste / alternative reaction with higher atom economyHigh % yield means a n efficient conversion of reactants to products, reducing waste of reactantsReduce toxicity of any reactants / productsMore efficient methodsUse renewable feedstockAlternative uses for CO2Expanded polystyreneAs a solvent – extraction of caffeineDry cleaning ................
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