!Chemistry*271,*Section*22xx* * University*of*Maryland,*College*Park*General*Chemistry*and*Energetics* Prof.*Jason*Kahn*Final*Exam*(200*points*total)* December*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:*Friday,*December*17,*11S2*Chem i st r y *1 1 1 0S1111*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[–(εi<ε0)/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!P(v)dv!=!Cv2exp(–mv2/2kT)! dS!=!(cp/T)!dT! cp!=!qp/dT!=!dH/dT!Chemistry!271,!section!22xx!Final!Exam,!12/14/10! 2/10!Score!for!the!page! !1.* Multiple*Choice*(24*pts)*(i;!4!pts)!The!half!life!t1/2!of!a!first!order!reaction!A!→!B!(a)!=!(ln2)/k.!(b)!=!{k([A]0)!2}–1.!(c)!=![A]0/k.!(d)!is!shorter!than!the!half!life!of!a!second<order!reaction.!(e)!none!of!the!above!(ii;!4!pts)!A!first<order!rate!constant!!(a) has!units!of!time–1.!(b) changes!during!the!course!of!the!reaction!as!the!reactant!is!depleted.!(c) cannot!be!faster!t han!diffusion<cont rol l ed.!(d) has!units!of!M–1s–1.!(e) none!of!the!above.!(iii,!4!pts)!The!function!of!Photosystem!II!in!plants!is!to!!(a) use!light!energy!to!reduce!NADP+!to!NADPH.!(b) collect!light!energy!and!deliver!it!to!Photosystem!I.!(c) oxidize!wat er!to!provide!light.!(d) re<reduce!the!reaction!center!of!Photosystem!I.!(e) reduce!water!to!maintain!a!basic!pH.!(iv,!4!pts)!Dissimilation!is!defined!as!(a) using!a!substance!as!a!terminal!electron!acceptor!and!making!no!further!use!of!the!product.!(b) reducing!a!substance!in!order!to!incorporate!it!into!biomass.!(c) nitrogen!fixation!and!other!processes!that!split!diatomic!molecules.!(d) disguising!(one's!intentions,!for!example)!under!a!feigned!appearance.!(e) none!of!the!above.!(v,!4!pts)!The!Third!Law!of!Thermodynamics!gives!us!a!reference!state!of!zero!entropy.!What!else!is!necessary!for!measuring!absolute!entropies!of!pure!substances!at!non<zero!temperature?!(a)!The!First!Law!of!Thermodynamics.!(b)!Measurements!of!heat!capacity!as!a!function!of!temperature.!(c)!Calculation!of!the!free!energy!of!formation!from!tabulated!data.!(d)!Enumeration!of!microstates.!(e)!We!cannot!measure!absolute!entropy,!only!changes!in!entropy.!(vi,!4!pts)!The!Steady!State!Approximation!!(a) is!not!useful!in!enzyme!kinetics!because!substrate!concentration!is!constantly!changing.!(b) can!be!applied!only!to!reactions!of!the!type!A!→!B!→!C.!(c) holds!only!at!equilibrium,!when!the!state!of!the!system!is!steady.!(d) includes!rapid!pre<equilibrium!as!a!special!case.!(e) is!applicable!to!the!product!of!any!rapid!reaction.!Chemistry!271,!section!22xx!Final!Exam,!12/14/10! 3/10!Score!for!the!page! !2.* Heat*Capacity*(20*pts)*The!graph!at!the!right!shows!the!absolute!entropy!of!benzene!as!a!function!of!temperature.!(a;!6!pts)!Label!the!boxes!in!the!graph!with!the!physical!process!that!is!occurring!at!the!indicated!vertical!segments.!(b;!9!pts)!For!a!given!gas!and!temperature,!think!about!what!happens!when!the!gas!is!heated!at!constant!pressure!vs.!constant!volume.!Why!is!the!heat!capacity!at!constant!pressure!(Cp)!greater!than!the!heat!capacity!at!constant!volume!(Cv)?!!!!!!!!(b;!5!pts)!The!enthalpy!change!for!a!reaction!is!usually!obtained!from!the!slope!of!a!van’t!Hoff!plot.!How!can!we!tell!from!a!van’t!Hoff!plot!if!a!reaction!has!a!non<zero!∆Cp?!!!Chemistry!271,!section!22xx!Final!Exam,!12/14/10! 4/10!Score!for!the!page! !3.*Photosynthesis*and*atmospheric*chemistry*(40*pts)*(a;!15!pts)!Why!have!plants!as!well!as!our!eyes!evolved!to!be!sensitive!to!the!wavelengths!that!we!have!so!egocentrically!named!“visible”!light?!Before!the!advent!of!photosynthesis,!what!was!different!about!the!spectrum!of!light!reaching!the!earth,!and!why?!Why!was!there!no!life!on!land!at!the!time?!!!!!!!!!!!!(b;!16!pts)!Fill!in!the!blanks!Two!possible!failure!pathways!for!photosynthesis!are!________________________________________________,!if!the!electron!is!not!transferred!away!from!the!excited!state!fast!enough,!or!__________________________________!__________________________________________,!if! the!el ectron! is!not!removed!from!the!immediate!vicinity!fast!enough.!For!an!artificial!solar!cell!to!be!useful,!after!charge!separation!the!electrons!must!re<reduce!the!reductant!only!after!traveling!through!the!_________________________________________________________.!The! excited! state! chromophore! of! Photosystem! I! is! a! very! strong! _____________________________________,!whereas! Photosystem! II! generates! a(n)! _____________________________! that! is! strong! enough! to! remove!_________________________!from!___________________________!and!generate______________________________.!Chemistry!271,!section!22xx!Final!Exam,!12/14/10! 5/10!Score!for!the!page! !(c;!9!pts)!How!does!increased!atmospheric!CO2!cause!global!warming?!!!!!!!!4.*Kinetics*and*Thermodynamics*(45*pts)*(a;!7!pts)!The!Maxwell<Boltzmann!distribution!and!Arrhenius!equation!state!that!the!rate!of!an!elementary!reaction!always!increases!with!increasing!temperature.!So!how!is!it!possible!for!the!equilibrium!constant!of!a!reaction!A!⇌!B!to!decrease!as!temperature!increases?!Would!the!reaction!be!(circle!one)!!!!exothermic!!!!!or!!!!!endothermic?!!!!!!Chemistry!271,!section!22xx!Final!Exam,!12/14/10! 6/10!Score!for!the!page!
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