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Unformatted text preview: Last Name First Name KEY Lab Sec. # ; TA: ; Lab day/time: Andreas Toupadakis, Ph.D. Fall 2006 CHEMISTRY ZC Section A EXAM 2 Instruct/hm: CLOSED BOOK EXAM! No books, notes, or additional scrap paper are permitted. All information required is contained on the exam. Place all work in the space provided. If you require additional space, use the back of the exam. A scientific calculator may be used (if it is a programmable calculator, its memory must be cleared before the exam). This exam has 11 pages total. (1) Read each question carefully. (2) For Part I there is some partial credit. There is no partial credit given for part II. There is partial credit for part III. (3) The last 2 pages contain a periodic table and some useful information. You may remove them for easy access. (4) If you finish early, RECHECK YOUR ANSWERS! 13.a b 14.a b E; 0' n0 an. an U.C. Davis is an Honor Institution CL N [email protected] c 17. a b 18. a 19.a b c Earned Points /24 /36 /15 /25 Possible Points # 1-12 # 13—21 # 22 (15 points) # 23 (25 points) (2 points each) (4 points each) @ 0' n @n [email protected] ®[email protected] 21.a b c /100 Total Score (100) 13-21 ram/poms: Name Exam 2 (Page 2 of H ) Part I: Concepts (2 points each) Some partial credit is available 1. Complete and balance the following reaction: Kcs) + 02(9) a kolm 2. Complete and balance the following reaction: + 01(5) tlHZOU) *t Cc: Coqx * lOHYU-qx \- \—\z (gl 3. Complete and balance the following reaction: L\ A|(s) + 302(9) 6 ‘1 (M7, 0 v, (a 4. Complete and balance the following reaction: 5iC|4(9) + 1H2(g) —> Q: (0 Jr q \x 02 (3x 5. Give the two reasons why the compound NF5 does not exist but PF5 does. (0\ Nilvozéev‘ glow is §WOpg€r *MOW pMosplnovug glow. \Vt \Al'lV’O‘AeW C09: Ehflupnutows Woww be Grounded. Clem «foam. ,, .. LbVll" glow \nog d {\O. Ovcxleob‘efl ’Qo‘r bOMGlMa‘ N (3er incl. 6. What is aqua regia? A \AAKthNe, 0{ Come. l\(fl(uq\ CLViG Come. HNOacq“ \\A Q :Sil Yo¥<0 by vo-euwe‘ 7. Is the compound N204 paramagnetic or- 8. Draw clearly the structure of P4010. \ Name Exam 2 (Page 3 of ’l 1) 9. WriTe The balanced chemical equaTion for eTching glass made from SiOz wiTh hydrofluoric acid, producing silicon TeTrafluoride gas. Q1010) {7 L\“C(0q\ ”*9 <iCu(3\+ illeCzl 10. Which of The Three acids: H3POZ, H3P03 or H3PO4 is a diproTic acid? HSPOg 11. When chemisTs sTudy chemical reacTions, They ask Three fundamenTal quesTions. WhaT happens? To whaT exTend does iT happen? Tl" e YW‘ 03 ‘l vaw' c. S How fasT does iT happen? k; “Q h C C § Each of The lasT Two quesTions can be answered wiTh one word, indicaTing The field of science ThaT gives The answer To The quesTion. Give The words. 12. Give The uniTs of The raTe consTanT for a Third order reacTion. Name Exam 2 (Page 4 of 11) Part II: Short Calculations (4 points each) No partial credit (right or wrong) 13. Consider the reaction: 4 PH3(g) —> P4 (9) + 6 H2(g) If the [H2] increases from 0 M to 3.0 M in 60 sec; What is the rate of the reaction? What is the rate of disappearance of PH3? a. rxn rate = 0.0083 Ms'l rate of disappearance of PH3 = - 0.033 s“ b. rxn rate = 0.0083 Ms rate of disappearance of PH3 = - 0.033 Ms1 C. rxn rate = - 0.0083 Ms" rate of disappearance of PH3 = - 0.033 Ms"1 d. rxn rate = 0.0083 Ms'1 rate of disappearance of PH3 = 0.033 Ms’1 e. rxn rate = 0.0083 Ms'1 rate of disappearance of PH3 = - 0.033 Ms'1 [Stilt-3 \ (%.O~O)N -l— ._...__——— — : "‘ QQ'\€ OE disguPP. Of Wk 1 ’ Ll (WV‘ YO“) C ’L‘ x 0' 0093 :’ 00%; M Sp" 14. For the reaction: CZH4Br2 + 3KI —> 62H4 + ZKBr‘ + KI3 Initial rate data at 60°C are: [CZH4Br2] [KI] A[KI3]/At (M/min) 0.500 1.80 0.269 0.500 7.20 1.08 1.50 1.80 0.807 The rate law is: a. rate = k[Czl‘l4l3f‘2][KI]3 b. rate = k[KI] c. rate = k[C2H4BI‘2][KI] d. rate : k 2. rate = k[C2H4Br‘2] Name Exam 2 (Page 5 of 11) _____________——__________._._—————————— 15. DaTa for The reacTion: A + B —> C are given below. Find The raTe consTanT for This reacTion. ExperimenT [A] [B] IniTiaI raTe (M/s) 0.030 0.060 2.5 x 10'5 2 0.030 0.020 2.5 x 10'5 0.060 0.060 10.0 x 10'5 || k = 2.8 x 10'2 M‘ls‘1 . k : 2.8 x 10-25-1 . k = 9.2 x 10'2M'ls'1 . k = 4.5 x IO'ZM'Zs'l . k = 4.5 x 10‘2Ms'1 NQGO'D Qale 4: k [931(33'30: PCNXI Av» l4: (20AM [A31 -5 ~i - \ : 1.6fil0 NS : 1.8300 Zquq. 0.0301 M1 16. The reacTion A + B —> C + D is second order in A, and zero order in B. The value of k is 0.012 M_1 min—1. WhaT is The raTe of This reacTion when [A] = 0.125 M and [B] = 0.435 M? a. raTe = 6.2 x 10'5 M min'1 b. raTe = 1.9 x 10'4 M rnin'1 c. raTe = - 3.5 x 10'5 M min'1 d. raTe = 6.8 x 10'20 M min'1 e. raTe = 5.2x 10'3 M min'1 (L _ QOSFC ': L< [Al 2 (0.0\'L [\A lw;m'l\(0‘\1§-M\L: LO) XlO—ll N vwvx—l 17. The firsT order reacTion A —> producTs has TU2 = 150 sec. WhaT percenT of The sample remains unreacTed afTer 300 sec? a. 10% b. 78% o c.40°/o A’ETQY \§O §€C M €0/o cmveocled d. 25% e. 30% . l\/€\€Y lgo §€< Oddlliomové N Lgouo :_ Z 3 QCK uvweocled. Name Exam 2 (Page 6 of 11) 18. 19. Q. 20. 1M 21. If a reaction is first order with a rate constant of 5.48 x 10'2/sec, how long is required for 3/4 of the initial concentration of reactant to be used up? a. 67.8 sec b. 3.69sec £:Q£”L 31X 0.692 :Qx (16653 c. 25.3 sec ,. _2, - d. 27.6sec k s‘Llex'O C ‘ e. 98.4 sec ‘: 1§_3 sec A reaction is first order. If its initial rate is 0.0200 M/sec and 25.0 days later its rate is 6.25 x 10'4 M/sec, then its half-life is: Cl. 'l'1/2 = 1.0 day b. T1/2=2~O dGYS Q t [4 C93 ) Q0 :0.0ZOO [Vléflz L C910 C. 11/2 3 3.0 days d. 1'1/2 = 4.0 days e. 1'1/2 = 5.0 dr-‘Y$ A; 4: 15‘_O dog; ) Q; IGflSXlOPull/ls-‘ :LCR—B ‘6 CM" _ L< g Q ‘ _ 0.64% [Flt Mg“ (1— _L.{ m \AcOJL‘ 5 Lh~Molq The first-order reaction A —> Products has a half-life, rm, of 55.0 min at 25 °C and 6.8 min at 100 °C. What is the activation energy for this reaction? a. 34.2 kJ mol'1 b. 25.8 kJ MOI-1 T ~: 1%8.\C K (fit/1)‘ :S’€—I O burn c. 78.3 kJ mol'1 ) d.38.9kJmol'1 ’ll :z’izAs l< , (6,151: 6.8 mm" e. 12.6 kJ mol'1 L. e... \ {,110'6‘53fal/1l a. l\ —— v, ’— k7. R TL T; ({,,L)‘ Q TL ’(u In the first order, reaction A —+ products, [A]: 0.400 M initially and 0.250 M after 15.0 min, at what time will [A]: 0.200 M? a. 45.6 min b. 6 .5 i ‘ 083.8214: JG :0 , [A10 : O-Lioom d. 34.5 ' ._ g~ a : ‘ e. 22.1m:\‘in e \ O W‘ n ’ [91% O 1§O M L: 0.01% Cm-T Name Exam 2 (Page 7 of '14) ParT III: Long Answers Please show all work for calculations - ParTial crediT may be given 22. (15 poinTs) Given The following informaTion for The reacTion: 2N0 + Oz ——> ZNOZ RATE (M/s) 0.050 a) DeTermine The raTe law expression for The reacTion. b) DeTermine The value of The r'aTe consTanT. c) DeTermine The raTe of The reacTion when [N0] = 0.020 M and [02] = 0.020 M. a) RaTe law expression: Rate = k LN 0’3 [0331 6“). ’l ow) Ll glnows ’lml ovdev dependence On E011 éfp. ’1. gm} 2. ‘* ls-l OYdev dep-emdemu 0“ [N03 — Ll '7— -l b) RaTe consTanT: k - ijxlo N g Av“, 'CjPfllw’t’W‘l Q : L [NOXEQAL So ’Qov ‘91“). i I 0.0§O 3 1" CO'OHqAQO-OZOVL "‘3 \K : l3xlol‘ “(29" c) RaTe of reacTion: Rafe =O.lO.SAi , , ‘L Qulc : ([3 ’XIOL‘ MIC” (COLON) (0.010 M\ : : O.lO M<fl4 Name Exam 2 (Page 8 of 44) 23. (25 poinTs) Formic acid (HCOOH) decomposes in The gas phase aT elevaTed TemperaTures as follows: HCOOH (9) —> 602(9) + Hz(9) The decomposiTion reacTion is deTermined To be firsT order. A graph of The parTial pressure of HCOOH versus Time for decomposiTion aT 838 K is shown as The Top curve in The figure below. Pressure (Torr) HCOOH 150 0 500 1000 Time (3) When a small amounT of solid ZnO is added To The reacTion chamber, The parTial pressure of acid versus Time varies as shown by The lower curve in The figure. a) Using The above graph calculaTe The firsT-order raTe consTanT for The decomposiTion of formic acid, before ZnO is added. b) WhaT can you conclude from The effecT of added ZnO on The decomposiTion of formic acid? c) The progress of The reacTion was followed by measuring The poTenTiaI pressure of formic acid vapor aT selecTed Times. Suppose ThaT, insTead, we had ploTTed The concenTraTion of formic acid in uniTs of moI/L. WhaT effecT would This have had on The calculaTed value of k? d) The pressure of formic acid vapor aT The sTarT of The reacTion is 3.00x102 Torr. Assuming consTanT TemperaTure and ideal—gas behavior, whaT is The pressure in The sysTem aT The end of The reacTion if The reacTion is 100% yield? If The volume of The reacTion chamber is 436 cm3, how many moles of gas occupy The reacTion chamber aT The end of The reacTion? e) If AH ° for The overall reacTion is -15 kJ/mol and The acTivaTion energy E, for The reacTion is 184 kJ/mol, skeTch an approximaTe energy profile for The reacTion, and label AH °, Eu, and The TransiTion sTaTe. Exam 2 (Page 9 of 11) Name -3 _, a) Rate constant = \. LI x 10 g - .6 k 9.5:; now we 3W ihzgoo s b) Conclusion: ZWO OctS cs 0. CULVUth. c) What effect? d) Pressure = f ' Moles = 6.00m0'3 woées‘ P\i Z \n (2T .J, \n: 0V :CGOO #*OYV\<1"U*UW\LEEGE> , QT (Q 081\ Ldtw _.___,\(82%k) Wo~e' k 2: 5.00 XIO' MAO-Q1 9. e) The reaction profile: TYOW§i #80“ C +Q\'C => Pemwe emevgj Name Exam 2 (Page 10 of 11) Some useful equations and constants: PLEASE NOTE: Important values and equations required for calculations are given with the respective problem. The following may or may not be of any u5e. Constants: R = 8.3145 J / mol K NA = 6.022 x1023 latm = 760 torr R = 0.0821 L atm / mol K h = 6.626 x 10'34 J s 1nm = 10'9 m 1 L = 1000 cm3 Equations: Slope : Ay/Ax TK = Toc + 273.15 ToF — 32 = 1.8 ToC Eu AG°=AH°—TAS° AG=AG°+RT1nQ AG°=—RT1nKeq k=AeW PV =nRT lnflzE—“[i—i] k2 R T2 T1 rate = k[A]0 = k [A]! =— kt + [A]0 Q = [:11]C0 We = k[A] 1n[A], = —kt+ln[A]O ’; = 2:93 rate = k[A]2 L = kH 1 ti = 1 [A1, [A10 2 k[A]0 M 0m NEENN EN N.NENENNNEEESNNNOE/$82NNEN.NaéaiNez £3 E N 2; o: NNNN .2 32 E36 SEN N: NEENNN NNNNEWSBEEE :3 N: NN N .32 .2 5:2 .szNNo 53 ENE 5N 8&2: >3N<NQNQDNE§oméiqfionoéaBtdtn 8on onNZ waging Nuns mammmE U<NNDN mNNN NNNNNNN 5E5 gm> Nam NNNNN ANNNN NNNNN NNNNN NN NNN NNNNN NNNNN ANNNN NNNNN NNNNN NNNN NNN NNNNNNNN NNNNNNN ggaaaaaaaalaa NE SN 2: N NN NoNNN NNNNN NS N NE NNNNN NS NN N3 NNNNN NNN NN NNN NNN NNN NN NNN @va NN. 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