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105bs10_warshel_e1_key

105bs10_warshel_e1_key - Chemistry 105bL PLEASE PRINT YOUR...

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Unformatted text preview: Chemistry 105bL . PLEASE PRINT YOUR NAME IN BLOCK LETTERS - First Letter of EXAM #1 as am Name: February 04, 2010 Professor Arieh Warshel Last 4 Digits SID#: Lab T.A.’s Name: Lab Day and Time: Please Sign Below: I certify that I have observed all the rules of Academic Integrity while taking this examination. Signature INSTRUCTIONS: 1. Please show all of your work to receive fi111 credit. 2. There are 5 problems on 7 pages. Please count them before you begin to see that you have a complete exam. Some useful equations can be found on the last page. 3. If necessary, please continue your solutions on the back of the preceding page (facing you). 4. You MUST submit all pages to the proctors, including the periodic table page. Put your name onto the equations page in the space provided. 5. You MUST use black or blue ink in order to be eligible for any regrades. (No whiteout, no erasable ink, no pencil.) 6. Only a Casio FX—26O calculator may be used on Chem lOSa/b exams. 7. Turn off cell phones and other electronic communication devices and put them away, out of sight. They may not be taken out of your bag during the exam. 8. When time is called, stop working on your exam immediately, turn the exam over and pass it to the aisle. 1. (20 points) The initial rate of a reaction A + B —> C was measured for several different starting concentrations of A and B, with the results given below: .(a) Using these data, determine the rate law for the reaction. 771$ only 2 exffs “0% a, an“. I}: WW are, flyfcfir/‘A'vj. Rtt/ /./&'3 Ms" ,4 9.7214 M 353-44 41 M. Edi? =2.0/1Ij$" '46. 0’7274, (6.202. = 0.573 - 0573 // @= _-r.~H Wits?) A (b) What is the value (and what are the units) of the rate constant k? mmyev: bk Mam—I a ~2 ”/ Cat/“LBJ m 0.335M s (c) What will be the initial rate when [A]0=0.10 M and [B]0=0.10 M. @ Rafi=[0-335&"2s")(o.lo E)l(o.l0fj) =i333/V6—4—M s“ l ((1) Consider the reaction A + B + C 9 D The rate law for this reaction is Rate = (k[A][C]2)/([B]1/2) Suppose the rate of the reaction at certain initial concentrations of A, B, and C is 0.0115M/s. 0 What is the rate of the reaction if the concentratio of A and C are doubled and the concentration of B is tripled? A 77 2. (20 points) I The reaction, A+B -> C has a rate constant of 2. 3 L mol'1 sec at 6500K. The rate constant increases to 66 L mol'1 sec at 8000K. 22. (a) What 1s the activation barrier of the reaction? ,4» “£3- ; :E‘:[J_- L): '%—%'—( :MJ .flxnflfi “M’s" ”.5 5-55 Wk 2.3M'IS'I =4 227: 3 34" - 33/9‘7 ”(k V fwxéfb K1 __ -334 x 7. 2w J'mul'flt‘l __ ¢ - 5" ”2'33X/odfk” ' 9.67/6/0 J—M‘é / ~/ 0’ 9g . 7 1 TM (b) What will the rate constant be at 0 K? 00 flag &5 w) i=01§zwfll¢fiMLI f @ a2 212,52.» 2-1. -emx/WM’ 2-2. ”‘7 K 7; 7/ mm J’M"k" ° W" \ 1.3 /Z1 ’41 2 “’00 A; = 0 ,0 (c) What will the rate constant be at 20,000,000 K? /, ‘9 %&-'§s(J——L —"7“9”°4~7'M" _/___ .1. “17.9% AT: *7 K TL 77 " 2.14;: + I73} 3 A... 2.5 5”” — Hxxo M’s” (d) The reaction A + B 9 D has an activatio arrier of 20 kJ/ 1 s'1 at 300K. What is the frequency factor? AA 75.“: +3,“ -,2o)</o 317m!" ’6”: 0 = (3 alsta'mW/CQfin/a) +AA a rate constant of “3.0/9 +€.0/7:%£’$ 3 /+= (4- ./ 3. (20 points) (a) Circle “True” or “False” for each of the following: (i) The rate constant of second order reactions True 7"— depends on the concentration. + (ii) Arrhenius believed that rate constants are independent True False 7’f of time. I 1L (iii) Integrated rate laws describe the dependence of the rate True F on the concentration. 7(— (iv) Enzymes accelerate reactions by increasing the energy True @ of the reactants. 2F+ (v) The Haber process helped to both save people and kill people. True False True 9, 7‘- (vi) The mechanism of chemical reactions can be determined P uniquely by knowing the balanced chemical equation. [ Pf (vii) Arrhenius grade for his PhD examination was C. Q False (b) Derive t1/2 for a zero order reaction (find the relationship between t1/2, [A0] and k). EA]. , [A], = (A2: “it Dr], , [AL =- r/ré/t, /2 '£ [A]. = vé 2:,1 .6 V7, = i [A]. «é ._. {A}. 2k (c) The reaction A+B+C '9 D involves only a single step. What is the molecularity of this reaction? @@ Answer: MALL—— 4. (20 points) (a) The enzyme, carbonic anhydrase, uses the Zn2+ metal ion to catalyze the reaction: I '5 “WOh/C'ID III MW. #11 0H” [shy/13¢ if) Mum Iffirms. How do you think the enzyme catalyzes the first step of the reaction (I 9 II) by using the Zn2+ metal lon— where does it place the Zn2+ ion? Explain. Zh2+ Sfi‘I/Ises +£L 0H_ ”.1 +4: @ Musi'fl‘w‘» “all?" k1 (b) A given reaction Av- :8 has an energy profile of the form 1 Which reaction constant will 1ncrease faster with temperature, /. k1 or k- ? Please explain. ta," Note: k1 or k. 1 are for the forward and backward reactions, respectively. Assume that the frequency factor is identical for k1 and k4. glue. ELM) > E411) H’ will be ,é., W Increases fisfzr 7‘5”,” 4Q .12- M 7—7‘. (M72: kWh/35‘ R’lnilf/é— Av; nm‘éraznfi do 1.40% M13 him—fies? rob/em J (c) In any lti step reaction mec 15m, the rate of the overal eaction lS determined by the rate of the ————— step in the mechanism. (circle the answer) a) first @ @ b) last d)‘: 5. (20 points) The following mechanism has been proposed for the reaction between a metal fluoride and fluorine: Step 1: MF2 + F2 -) ,M‘F4/ (fast equilibrium) Step 2: gym/ware Mr? (slow) Step 3: W + MF2 9 M2F6;F2/ (fast) (a) What is the overall reaction? (b) What are the intermediates in this reaction? @ M F“ 2 M F6 (c) Which is the rate—determining step? (9 We? 7— (d) What is the molecularity of the rate-determining step? @ Limo/6W (e) What is the rate law predicted by this mechanism? (Please show work.) firm $1610 $1919, mi'e = 1 CM Flt] [Ft] L‘fiwo e“ - = raft. reverSe {Nb firs" (f) The reaction 2NO2 + F2 = 2NO2F has a rate law of Rate = ' ‘ I2 2 . Please suggest a mechanism that describes this reaction. S’tefb Now FL 9 N02): 7‘ F /5'/aw) @ N°2+ F -—> Nod: [19:74) Name: E Submit this page with your exam. All answers should be in the space provided with each question or on the back of the previous page (facing the question). USCfiJl Physical Constants and Equations: Avogadro's number Universal gas constant Faraday's constant Ifax2+bx+c=0 PV=nRT nw=q§ AS=k In W AG==-nFE_, AG=AG° + 12ng AG=AH-TAS E=q+w AG" "RT aneq E=hu=rnc2 then x = N = 6.022 x 1023 [1101'1 R = 0.08206 L atm K“ mo!" = 8.314 I K" moi" F = 96,485 C moi" ~bzt bz-4ac 2a KJKC = (1mm Order Integrated rate law Zero [A], - [Ala = -kt First lnlA]t = ln[A]0 — kt Second l/[A], = l/[Alo + kt ln(k) = %—[%)+ ln[A] ~41? = —-A-1l:{—+AS ...
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