!Chemistry*271,*Section*22xx* * University*of*Maryland,*College*Park*General*Chemistry*and*Energetics* Prof.*Jason*Kahn*Final*Exam*(200*points*total)* May*14,*2010*You!have!120!minutes!for!this!exam.!!Exams!written!in!pencil!or!erasable!ink!will!not!be!re<graded!under!any!circumstances.!Explanations!should!be!concise!and!clear.!I!have!given!you!more!space!than!you!should!need.!There!is!extra!space!on!the!last!page!if!you!need!it.!You!will!need!a!calculator!for!this!exam.!No!other!study!aids!or!materials!are!permitted.!Partial!credit!will!be!given,!i.e.,!if!you!don’t!know,!guess.!Honor!Pledge:!At!the!end!of!the!examination!time!,!please!write!out!the!following!sentence!and!sign!it,!or!talk!to!me!about!it:!“I!pledge!on!my!honor!that!I!have!not!given!or!received!any!unauthorized!assistance!on!this!examination.”!!!!!**Your*Name:* **Your*SID*#:* *Viewing:****Monday,*May*17,*9:30T10:30*a.m.,*Chemistry*1112*(Wing*1)* *Useful*Equations:*∆S!–!q/ T!≥!0! pH!=!–!log([H+])! S!=!klnW!∆G°!=!–!RTlnKeq! ∆G!=!∆H!–!T∆S! PV!=!nRT!Ka!=![H+][A–]/[HA]! ni/n0!=!exp[–(Ei<E0)/kT]! ∆G!=!–nℱE!°C!=!°K!–!273.15! R!=!8.314!J/mole!K! E!=!E°!–!2.303(RT/nℱ)log10Q!2.303RT/ℱ!=!0.0592!Volts!at !25!° C ! ℱ!=!96500!C(oulom b )/ m o le !Standard!hydrogen!electrode:! 2!H+!(aq,!1!M)!+!2!e–!→!H2!(g)! E°!=!0.000!V!lnKeq!=!–∆H°/RT!+!∆S°/R! ln!k!=!(–Ea/RT)!+!ln!A! 1!Volt!=!1!Joule/Coulomb![A]!=![A]0!–!kt! ln[A]!=!ln[A]0!–!kt! 1/[A]!=!1/[A]0!+!2kt!Chemistry!271,!section!22xx!Final!Exam,!5/14/10 2/11 Score!for!the!page! !1.* Multiple*Choice*(30*pts)*(i;!5!pts)!The!half!life!t1/2!of!a!second!order!reaction!A!+!A!<>!B!(a)!=!ln2/k.!(b)!=!{k([A]0)!2}–1.!(c)!=![A]0/k.!(d)!is!shorter!than!the!half!life!of!a!first<order!reaction.!(e)!none!of!the!above!(ii;!5!pts)!A!first<order!rate!constant!!(a) has!units!of!time–1.!(b) is!inversely!related!to!half<life.!(c) depends!on!reactant!concentration.!(d) has!units!of!M–1s–1.!(e) (a)!and!(b).!(iii,!5!pts)!The!function!of!Photosystem!I!in!plants!is!to!!(a) use!light!energy!to!oxidize!carbon!dioxide.!(b) use!light!energy!to!reduce!NADP+!to!NADPH.!(c) oxidize!wat er!to!provide!light.!(d) re<reduce!Photosystem!II.!(e) oxidize!water!and!transfer!electrons!to!H+.!(iv,!5!pts)!Syntrophy!is!defined!as!(a) consumption!of!the!product!of!the!reduction!of!one!microbe’s!terminal!electron!acceptor!by!another!microbe!for!their!mutual!benefit.!(b) any!interaction!among!microorganisms!that!live!in!the!same!environment.!(c) microorganisms!that!make!synthetic!chemicals.!(d) [deleted!bad!pun!on!Sin!Trophy]!(e) pathogens!that!co<infect!target!hosts.!(v,!5!pts)!Stratification!of!inorganic!NO3–,!SO42–,!and!other!species!in!the!water!column!or!in!sediments!originates!because!(a)!anaerobes!are!heavier!than!aerobes!so!they!sink.!(b)!sulfate!and!nitrate!react!with!metals!in!the!soil!so!they!are!present!only!near!the!top.!(c)!weathering!and!currents!leach!out!different!ions!at!!different!depths.!(d)!at!any!depth,!the!organism!that!is!capable!of!using!the!best!available!terminal!electron!acceptor!dominates,!so!the!other!terminal!electron!acceptors!are!left!alone.!(e)!None!of!the!above.!(vi,!5!pts)!The!fundamental!condition!for!applicability!of!the!Steady!State!Approximation!is!(a) The!product!concentration!must!be!zero.!(b) The!concentration!of!the!intermediate!cannot!change!at!all!during!the!reaction.!(c) There!must!be!a!rapid!pathway!for!decay!of!the!steady!state!intermediate.!(d) The!activation!energy!for!the!reaction!must!be!smaller!than!the!∆G°.!(e) The!reaction!must!be!second<order.!Chemistry!271,!section!22xx!Final!Exam,!5/14/10 3/11 Score!for!the!page! !2.* Short*Answer*(36*pts)*(a;!6!pts)!Give!two!statements!that!must!be!true!for!or!a!substance!to!be!called!a!catalyst!for!a!reaction.!!!!!!!(b;!6!pts)!Why!does!www.350.org!call!“350”!the!most!important!number!in!the!world?!!!!!!(c;!6!pts)!The!main!function!of!Photosystem!II!in!plants!is!to!provide!electrons!to!re<reduce!Photosystem!I.!What!is!the!oxidation!half<reaction!used,!and!why!was!that!choice! advantageous!during!evolution?!!!!!Chemistry!271,!section!22xx!Final!Exam,!5/14/10 4/11 Score!for!the!page! !(d;!9!pts)!What!is!a!“sustainability!wedge”?!Algal!biofuel!may!provide!one:!what!is!an!advantage!of!biofuel!in!general!over!wind/solar/nuclear!energy?!!!!!!!!!!!(e;!9!pts)!We!considered!the!temperature!dependence!of!rate!constants!in!light!of!both!the!Maxwell<Boltzmann!distribution!and!also!Eyring!theory.!Choose!one!and!briefly!explain,!qualitatively,!how!it!rationalizes!the!observed!form!of!the!Arrhenius!equation.!!Chemistry!271,!section!22xx!Final!Exam,!5/14/10 5/11 Score!for!the!page! !3.*Kinetics*and*the*Steady*State*Approximation*(50*pts)**Consider!the!reaction!NO2!(g)!+!CO!(g)!<>!NO!(g)!+!CO2!(g).!It!is!important!in!understanding!atmospheric!chemistry!of!air!pollution,!and!it!has!been!proposed!as!one!step!in!a!potential!series!of!reactions!that!could!be!useful!in!catalytic!converters.!(a;!4!pts)!This!is!a!redox!reaction:!what!is!the!oxidant!and!what!is!the!reductant?!!!!!(b;!4!pts)!Assuming!the!reaction!is!elementary,!write!the!differential!rate!law!for!the!production!of!CO2.!!!!!!(c;!8!pts)!In!the!1910s<1970s,!the!observed!activation!energy!for!this!reaction!was!determined!to!be!about!130!kJ/mol.!If!the!second<order!rate!constant!k!is!64!M<1s<1!at!1000!K,!what!is!k!at!500K?!!!!!!!!!!!!!!!!!!!Chemistry!271,!section!22xx!Final!Exam,!5/14/10 6/11 Score!for!the!page! !(d;!9!pts)!At!0.010!M!NO2!and!0.050!M!CO,!what!concentration!of!CO2!is!produced!in!10!minutes!for!a!rate!constant!k!=!2.4!x!10–5!M–1s–1?!You!can!assume!that!the!rate!remains!constant!for!this!time;!based!on!your!answer,!why!is!this!assumption!justified?![By!measuring!an!initial!rate,!we!avoid!the!need!to!use!an!integrated!rate!law!that!we!didn’t!learn.]!!!!!!!!!!!!!!!!(e;!9!pts)!For!use!in!practical!systems!at!reasonable!temperatures,!catalysis!of!the!above!reaction!by!gas!phase!metal!cations!“M+”!has!been!proposed,!according!to!this!scheme:!M+!+!NO2!→!M O+!+!NO!MO+!+!CO!→!M+!+!CO2!On!the!reaction!coordinate!diagram!below,!add!in!a!reasonable!curve!that!could!represent!the!above!catalytic!scheme.!!Chemistry!271,!section!22xx!Final!Exam,!5/14/10 7/11 Score!for!the!page!
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