18.1-lattice-energy

LatticeEnergyEnthalpychangeofatomisation(∆Hat:+)Enthalpychangewhen1moleofgaseousatomsareformedfromitselementsunderstandardcondition(25℃,1atm)eg:Li(s)→Na(s)→Cl2(s)→P4(s)→Enthalpychangeofionisation(∆Hi1:+)Enthalpychangewhen1moleofelectronsisremovedfrom1moleofneutralgaseousatomstoformonemoleofpositive(+1)gaseousionsNa(g)→Mg(g)→Enthalpychangeofionisation(∆Hi2:+)Enthalpychangewhen1moleofelectronsisremovedfromonemoleofpositive(+2)gaseousionstoform1moleofpositivegaseousionsunderstandardcondidiondefinitionoflatticeenergy,∆HLE:-Latticeenergyistheenthalpychangewhen1moleofanionicformedfromitsgaseousionsunderstandardcondition.E.g.Na++Cl-→NaClMg2++O2-→MgOExercise1:Writeequationsdescribingthelatticeenergyof(1)magnesiumoxide(2)potassiumbromide(3)sodiumsulfide(4)lithiumfluoride(5)calciumoxidefactorsSize:asthesizeoftheionincrease,thelatticeenergybecomeslessexothermicCharge:asthechargeontheionincreases,thelatticeenergybecomesmoreexothermicE.g.LatticeenergyMgONa2OMagnesiumionissmallerthansodiumion,thelatticeenergyofMgOislargerthanNa2OExercise2:ExplainwhymagnesiumcarbonatehasamoreexothermiclatticeenthalpythanbariumcarbonateExercise3:placethefollowingcompoundsinorderofincreasinglyexothermiclatticeenthalpyLi2OLiFMgOAnswer:LiFLi2OMgOLiFiscomposedofsinglychargedionssohastheleastattractionbetweenions,Li2OhasonedoublychargedionandMgOhastwodoublychargedionssohasthemostattractionbetweenions2definitionofelectronaffinity,∆Hea1:-thefirstelectronaffinity:istheenthalpychangewhen1moleofelectronsisaddedto1moleofgaseousatomstoform1moleofgaseous1-ionsunderstandardconditionE.g.∆Hea1F(g)+e-F-(g)S(g)+e-S-(g)∆Hea2S-(g)+e-S2-(g)Exercise3:(checkup-3)(a)suggestwhythe2ndand3rdelectronaffinitiesarealwaysendothermic(b)The1stelectronaffinityofsulfuris-200kJ·mol-1.Thesecondelectronaffinityofsulfuris+640kJ·mol-1.CalculateavaluefortheenthalpychangeS(g)+2e-S2-(g)(c)Writeequationsrepresenting:ithe1stelectronaffinityofiodineiithe2ndelectronaffinityofsulfur3Born-HabercyclesBorn-Habercycleisaparticulartypeofenthalpycyclesusedtocalculatelatticeenergy∆HLE=∆Hformation-(∆HatmNa+∆HatmCl+∆H1stIE+∆H1stEA)∆Hf[NaCl]=-411kJ·mol-1∆Hat[Na]=+107kJ·mol-1∆Hat[Cl]=+122kJ·mol-1∆Hi1[Na]=+496kJ·mol-1∆Hea1[Cl]=-348kJ·mol-1∆HLE=(-411)-(107+496+122-348)=-788KJ·mol-1Exercise4:DrawfullylabelledBorn-Habercyclesfor(a)MgO(b)Na2OExercise5calculateavalueforthelatticeenergyofmagnesiumchloride∆Hf[MgCl2]=-641kJ·mol-1∆Hat[Mg]=+148kJ·mol-1∆Hat[Cl]=+122kJ·mol-1∆Hi1[Mg]=+736kJ·mol-1∆Hi2[Mg]=+1450kJ·mol-1Answer:-2523Exercise6calculateavalueforthelatticeenergyoflithiumfluoride∆Hf[LiF]=-617kJ·mol-1∆Hat[Li]=+161kJ·mol-1∆Hat[F]=+79kJ·mol-1∆Hi1[Li]=+520kJ·mol-1∆Hea1[F]=-328kJ·mol-1Answer:-10494definitionofenthalpychangeofsolution,∆Hhyd,-Theenthalpychangeofhydrationistheenthalpychangewhen1moleofaspecifiedgaseousiondissolvesinsufficientwatertoformaverydilutesolutionE.g.Ca2+(g)+aq→Ca2+(aq)Cl-(g)+aq→Cl-(aq)Exercise7:(a)whyistheenthalpychangeofhydrationalwaysexothermic?(b)Writeequationstorepresent(i)thehydrationofasodiumionfactorsSize:thevalueismoreexothermicforionswiththesamechargebutsmallerionicradii∆HhydismoreexothermicforLi+thanforNa+Charge:thevalueismoreexothermicforionswiththesameradiibutalargercharge∆HhydismoreexothermicforMg2+thanforNa+thepolarnatureofwaterstabilisestheions,thegreaterthechargedensityoftheion,thegreatertheaffinityforwaterandthemoreexothermictheprocesswillbeExercise8:Explainwhythevalueof∆HhydofNa+ismuchmoreexothermicthan∆HhydforpotassiumionsExercise9:namethechangesassociatedwiththeequationbelowA)KBr(s)+aq→KBr(aq)B)K+(g)+aq→K+(aq)C)K+(g)+Br-(g)→KBr(s)D)Br-(g)+aq→Br-(aq)E)K(s)+1/2Br2(l)→KBr(s)F)K(s)→K(g)G)Cl2(g)→2Cl(g)H)C6H12O6(s)+6O2(g)→6CO2(g)+6H2O(l)5definitionofenthalpychangeofsolution,∆HsolTheenthalpychangeofsolutionistheenergyabsorberorreleasedwhen1moleofanionicsoliddissolvesinsufficientwatertoformaverydilutesolutionE.g.MgCl2(s)+aq→Mg+2(aq)+2Cl-(aq)+3.9kJ·mol-1NaCl(s)+aq→Na+(aq)+Cl-(aq)-55kJ·mol-1Exercise10:writeequationstorepresenttheenthalpychangeofsolutionof(i)potassiumsulfate(ii)zincchloride5calculateenthaloychangesinsolution∆Hθsol=∆Hθhyd-∆HθLEE.g:determinetheenthalpychangeofsolutionofsodiumfluorideusigthefollowingdataLatticeenergy=-902kJ·mol-1Enthalpychangeofhydrationofsodiumions=-406kJ·mol-1enthalpychangeofhydrationoffluorideions=-506kJ·mol-1Exercise11:9(a)DescribeandexplainhowthesolubilitiesofthesulfatesoftheGroupIIelementsvarydownthegroup............................................................................................................................................................................................................................................................[3](b)ThefollowingtablelistssomeenthalpychangesformagnesiumandstrontiumCompounds.(i)UsetheabovedatatocalculatevaluesofΔHsolutionforMg(OH)2andforSr(OH)2.Mg(OH)2...................................................................................................................ΔHsolution=.....................................kJmol–1Sr(OH)2...........................................................