Answer key to practice exams

Answer key to practice exams - . ~,; i:;~eo t~"Oii...

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~~,;; i:;;;~eot~"O·ii . breathe relax breathe relax. NA~Ethe relax relax breathe t::}e In-Class Kinetics Exam MW TTH 75 pts Please be sure to show ALL of your work for full credit! 1. Consider three reactions with different values of E act and ~H: Reaction Each kJ/mol ~H, kJ/mol 1 20 -60 2 10 -20 3 40 +15 a. Sketch a reaction energy diagram for each reaction, including labels: axes, E a , ~H, reactants, and products. Put all three diagrams on the same graph. Assume each reaction occurs in one step. (10 pts) ~ I ',-).os: S b. Assuming that all three reactions are carried out at the same temperature and that all three have the same frequency factor A, which reaction is the fastest and which is the slowest? Explain your answers thoroughly. (4 pts) 1/1 =- -1:1 Z S/~~P If A I'd ·l/t> Sn'I/t/ks I E a (:{- 2. Explain how each of the following affects the rate of a reaction (increase, decrease, no change). Be sure to EXPLAIN why (4 pts each) a. Increasing the concentration of a reactant that occurs in the step before the rate determining R I)J step. 1[1,r 7 -", l' ,r IL<,& IJ c-.{j/~"~ . 8-" L -I I j /~ / JJ . _ // Q l1'l~ f' SI ~ ~-f 1;. .e,. .., 'vJifl [.p1 vJ (' I, b. increasing the concentration of a reactant that occurs in the step following the rate determin7t N >i .;1,) "I f,A.p ~:,::-:;'~·~-:l l1fi:'{J (t\ ~,) /N 1 Chern 401 - In-Class Kinetics Exam, s08
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breathe relax breathe relax breathe relax breathe relax breathe relax breathe 3. The following data are obtained for the initial rates for the reaction: A + 2B + C ~ 2 D + E Expt fAl,M fBl, M rCl,M Initial Rate, M/sec .sJ 1<, ::: I C I 2 3 ..... ,..-: '-OJ 14 1.40 0.70 0.70 1.40 1.40.,. 0.70 J '" LOOt- 1.00 fr", 1.00 11.-' R l -- \ R z = 0.5 X R l ~ R 3 = 0.25 X R z I .$- ~t(v ./~"'itJ. 4 1.40 1.40 0.50~ I Rt - 16 X R 3 ::l. 5 0.70 0.70 0.50 .(;-J R s - ???? a. Determine the reaction orders with respect to A, B, and C. (9 points) ( \. , b. Determine the value ofR s in terms ofR l . (3 points) .. 4. You wish to test the following proposed mechanism for the oxidation ofHBr: '. . , c . .. -/,: .. { ~tep I: HBr + Oz ~ HOOBr . l;, ", ", \ step 2: liOOBr + HBr ~ 2 HOBr step 3: I-!0l:3r + HBr ~ HzO + Br2 'You find that the rate is first order with respect to HBr and first order with respect to Oz. You can not _detect HOBr amo~.s;the products. a. If the proposed mechanism is correct, explain which step is rate-determining. (4 pts) 5~1 = Mklci.f;t 1M I. ~ b. Explain if you canEov~he proposed mechanism from these observations. (4 pts) y~ !JOAJff ?~Vp ~ Alec4N"iP"'t / rt.<. CJv~ Sc<#oJ / f - TA;f t;)'-J(? 0 D AJ' f 00J ~ ~ - c. Explain if you can disprove the proposed mechanism from these observations. (4 pts) If 7J~ lid ~.d f/tR ;) c~ '. o..J
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Answer key to practice exams - . ~,; i:;~eo t~&quot;Oii...

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