key_exam_22new - Last Name Lab Sec TA Andreas Toupadakis...

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Unformatted text preview: Last Name Lab Sec. # ; TA: Andreas Toupadakis, Ph.D. Spring 2008 CHEMISTRY 2C Section B EXAM 2 Instrucf/bns: l<é‘/ First Name ; Lab day/time: 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 10 pages total. (1) Read each question carefully. (2) There is no partial credit given for part I and II. There is partial credit for part III. (3) The last page contains a periodic table and some useful information. You may remove it for easy access. (4) If you finish early, RECHECK YOUR ANSWERS! U.C. Davis is an Honor Institution Possible Points Earned Points —l # 01-10 (4 points each) / 40 j #11-14 (7 points each) / 28 #15 (12 points) / 12 _l # 16 (8 points) / 08 # L7 (12 point' 5) ALL— Total Score (100) / 100 Multiple Choice (circle one) 10. a 11 -14 total pal'nrs: Name SpringZOOB Exam 2 (Page 2 of 10) Part I: Concepts (4 points each) Some partial credit is available 1. The main reason that PCI5 exists but NH5 does not exist is: a) The valence shell of phosphorus does not have d orbitals. b) The valence shell of nitrogen has d orbitals. c) Phosphorus atom is larger than nitrogen atom. d) The valence shell of phosphorus has d orbitals. e) Nitrogen is more electronegative than phosphorus. ©AT2008$PR Consider the table be/ow and answer the follow/Mg two questions (2 and 3): Element Ionization Energy Standard Oxidation Melting Point (kJ/mole) Potential (V) (°C) Li 520 3.05 180 Na 495 Chase the correct and accurate (i.e. well defined) statement: a) Na is oxidized easier than Li. b) Na is stronger reducing agent than Li. c) Under standard conditions, reduction of H20(l) by Na(s) is more spontaneous than reduction of H200) by Li(s). d) Na(g) is stronger reducing agent than Li(g). e) None of the above. ©AT2008SPR The reaction of solid sodium with liquid water is more vigorous than the reaction of solid lithium with liquid water because: a) The reaction of solid sodium with liquid water is exothermic but the reaction of solid lithium with liquid water is endothermic. b) The melting point of Na is much lower than that of Li. c) Under standard conditions, reduction of H20(|) by Na(s) is more spontaneous than reduction of H20(l) by Li(s). d) Na(g) is stronger reducing agent than Li(g). e) None of the above. ©AT2008$PR 7Na_me SpringZOOS Exam 2 (Page 3 of 10) 4. Choose the correct statement: ©AT2008$PR a) The differential rate law enables us to calculate the rate of a reaction from the rate constant and temperature. b) The integrated rate law expresses how reactant and product concentrations depend on time. c) The half—life of a first order reaction depends on reactant concentrations. d) The half-life of a 2"d order reaction does not depend on reactant concentration. e) Zero order reaction means a reaction with a rate constant equal to zero. 5. Choose the incorrect statement: ©AT20085PR a) The elementary steps must sum up to give the overall reaction. b) The mechanism must be consistent with the observed rate law for the overall reaction. c) A single reaction step is not made up of simpler steps. d) A reaction intermediate is a chemical species that is formed and used up during the overall reaction. e) Intermediates can never be isolated. 6. Choose the incorrect statement: ©AT2008$PR a) Reaction rate is concentration change over time required for the change. b) Reaction rate is always a positive number. c) Rate of formation of a product is always a positive number. d) Rate of disappearance of a reactant is always a negative number. e) The units of the rate constant for a third order reaction is M‘ls'1 7 Choose the incorrect statement: ©AT2008SPR a) The exponents in a rate law depend on the reaction mechanism. b) The exponents in a rate law are determined experimentally. c) The higher the value of an exponent in a rate law the less sensitive is the reaction rate to a concentration change of that component. d) Both the reaction rate and the rate constant depend on temperature and the presence of a catalyst. e) In general the rate of a reaction depends on the concentration of reactants, but the rate constant does not. Name _ SpringZOOB Exam 2 (Page 4 of 10) 8. Choose the correct statement: @ATZOOSSPR a) Intermediates are far less stable than transition states. b) For an elementary reaction we still need to do experiments in order to know its rate law. c) Reaction mechanism is the sequence of reaction steps that defines the pathway from reactants to products. d) The rates of all chemical reactions increase as the temperature rises. e) A five-step reaction involves five transition states and five intermediates. 9. The reaction described by the chemical equation, COH2(S) + 2H20(l) -—> 2H2(g) + Ca2‘(aq) + 20H‘(aq) a) is a Lewis acid-base reaction but not a Bronsted Lowry reaction. b) is a Bronsted Lowry reaction but not a Lewis acid-base reaction. c) is a precipitation reaction. d) is a redox reaction. e) None of the above. ©AT2008$PR 10. Choose the correct statement: a) All physical states of oxygen are diamagnetic. b) Hypophosphorous acid is a diprotic acid. c) An aqueous solution of phosphine gas has a pH = 7. d) Red phosphorus is more reactive than white phosphorus. e) Aqua regia oxidizes silver but not gold. ©AT20085PR Name SpringZOOS Exam 2 (Page 5 of 10) ParT II: ShorT Calculations (7 poinTs each) No parTioI crediT (righT or wrong) 11. In a caTalyTic experimenT involving The Haber process, Nz(g) + 3Hz(g) —> 2NH3(g) The raTe of reacTion was measured as: RaTe = A[NH3]/AT = 2.0x10'4mol L'1 s‘1 If There were no side reacTions, whaT was The raTe of disappearance of hydrogen? a) — 3.0x10'4 mol L'1 5'1 b) + 3.0x10'4 mol L'1 s'1 c) + 2.0x10'4 mol L‘1 5'1 d) - 1.0x10'4 mol L’1 s'1 e) — 1.5x10'4 mol L’ls'1 Qg‘e: _ Mm} :__i_ dim] : +5, [LEA/HQ 0t 3 m 7, (ye AEHA ': ~3— MBENHKU : 2 (QOxio’L‘\mo( E‘s ) at 2 OJ: "=5 12. WhaT are The uniTs of The raTe consTanT, k, for a half order reacTion, when concenTraTions are expressed in mol/L and Time in s? a) mol L'“2 s‘1 I] ‘L b mol”? L-1/2 3-1 , L c)) mol“2 L'ls‘1 Q t \ [A1 d) mall/2 L-l/Z e) mol2 L'1 5'1 i LOT L‘ L< WE) / L Q -i , i/ "/L \moé'L “9‘ :Fmrvmg L L " VVWUvg' L- — 9“ _ :4— : W,” -, \Moe LIIL NEW 13. Sprin92008 Exam 2 (Page 6 of 10) SubsTance A reacTs according To a firsT order raTe law wiTh k = 5.0x10‘5 5“. If The iniTiaI concentration of A is 1.00 M, whaT is The raTe afTer 1.00 h? a) 4.2 x 10-10 M/s b) 7.9 x 10'5 M/s __ -» 5 ,4 - A c) 3.3x10'7M/s l< -5°O“l0 g t, Loula d) 4.2 x10'5M/s e) 6.7x10'9M/s [FY10 : 1.00/Vi (Dow/)0 : 1. lQQlc€+ : l< [Rip IMEAerT-‘Ll: l’ngA’lo ){23600S ‘6m [93% '- -<S.O HO~S§_.)(%600 s3 +«€m(1.ool [Mic :0839 M 30 Qa¥8e1(§.ox lobggTXOBAS'Ml 14. The complexaTion of Fez’wiTh The chelaTing agenT dipyridyl (abbreviaTed dipy) has been sTudied kineTically in boTh The forward and reverse direcTions. Fe2*(aq)+3dipy(oq) t: Fe(dipy)sz‘(aq) For The complexaTion reacTion The raTe of formaTion of The complex aT 25 °C is given by: RaTe : (1.45 x 1013 L3 mol'3 5'1) [Fez‘] [dipy]3 For The reverse reacTion, The raTe of disappearance of The complex is: RaTe : (1.22 x 10'45'1)[Fe(dipy)32*]. WhaT is The value of The equilibrium consTanT for The above reversible reacTion? a) 1.19x1017 b) 4.0x1o23 Q Q c) 4.0x1033 4: "- Y (ml €01. d) 5.0x1022 e) 2.0x1o28 ,. 7) - , , - U119 ><lOlg LWoe 3fifi'lLF‘ell3l:dlpx,jz : t (,1.1Lxm””<~‘) [Fdamylfi] Md M: '3‘. /1+ ‘3 1 L339} WM 1 : l.L\§x\o :LlCleOl : l’<€‘1r lFell/lEGTPvFXZ L’L'L XIO'L‘ que SpringZOO8 Exam 2 (Page 7 of 10) Part III: Par'l'ial credit may be given Please show all work for calcula'l'ions 15. (12 points) Give The sTr'uc’rures of The following four chemical species: Name Sprin92008 Exam 2 (Page 8 of 10) 16. (8 points = 4+2+2) The reaction of nitric oxide with hydrogen at 1280 °C is: 2NO(9) + 2H2(9) —> N2(9) + 2H20(g) From the following data collected at this temperature: 0) Determine the rate law expression for the reaction. b) Determine the value of the rate constant. c) Determine the rate of the reaction when [N0] = 12.0x10'3 M and [H2] = 6.0x10‘3 M. EXP l [NO] (M) l [H2] (M) Initial Rate (M/s) l 1 5.0x10’3 2.0x10'3 1.3x10‘5 l 2 10.0x10'3 2.0x10'3 l 5.2x10‘5 3 l 10.0x10‘3 l 4.0x10'3 l 10.0x10'5 a) Rate law expression is: ’2. CYUVM —€¥p‘ ’3. omd ‘1 m Q o( [N01 Row 0-9.1de A» Q <>< [H13 if; Q a [NO/liltl—lzl "L MW M b) Rate constant is: FYOW gy p 1 l<: Ydt€ _. some"S M/s _ [NO’XJ‘CHA ClO-OX\O’KN\L(2.OMOJM) l k = 2.5x102M'2 -s'1 j - ' -3 RuleiCl‘SXiOl/Vi Z~Sml)(\l~0xloung 1(GM \0 Nl Rate = 2.2x10’4 M/s c) Rate of reaction is: Name SpringZOO8 Exam 2 (Page 9 of 10) 17. (12 poinTs) Deduce raTe law expressions for The conversion of Hz and I2 To HI aT 400 °C corresponding To each of The following Three mechanisms: (a) He + I2 —> 2HI (one sTep) (b) Ia 1—, 2I 21 + H2 —> 2HI (slow) (c) 124:,21 I+H2 S IHZ IHz + I —+ 2HI (slow) (d) Can The observed raTe low expression, raTe = k[Hz][Iz] disTinguish among These mechanisms? (0) RaTe = k[Hz][I2] ’1 (3’6 QU‘TC: l4; [Illtllt—k L Q4: Qv »——> l<i [113 = l'<-l Cf} «aw , _.,, [123 l/. Q0\€=l’<x l/n [HAEILU T2 2 (C) (205(61 l'<3[:l'\1:3[1] keepi : El -—) [131 I Rea/1 [Ill [L] keg}; : [IRA ,___) [IRES : (Kegw z [Hz/l [:3 V [HERA lz’ule 2 k3 l<€q,1, Elli.) quA [[11 3 _ 2W . km . p3 [m cm N2 ‘2 (d) Yes or Please circle one. QQTQ Name SpringZOOS Exam 2 (Page 10 of 10) 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 use. Constants: R .2 83145 J / mol K NA = 6.022 x1023 latm = 760 torr‘ :2 : 0.0821 L atm / mol K h = 6.626 x 10'34 J s 1 nm :109 m 1 L = 1000 cm3 Equations: Slope : Ay/Ax TK = Toc + 273.15 ToF — 32 = 1.8 Toc La A~i1°:AH°—TAS° AG=AG°+RTan AG°=—RT1nKeq k=AeRT Pl/ : nRT 1n5 = E“ [i—i] k 2 R T2 T: "W : “[410 = k [A], =-kt +[A]0 t2 = [:11]: mic : HA] 1n[A]I= -kt+ln[A]0 t2 = 0:93 we : kW L = 16+ 1 ,1 2 1 [A], [A]0 2 k[A]O 2 vAl ‘ 2| ‘ 50 ii (:34 : 44.95501» 7061 50.9415 51. w 46 .u r Nb 261935115 o22| 922mm; 9. 96) 74 75 ll’f Ta W R 1.139055 mm 1309479 1.1.3.4 ms. 104 “)5 Rt Db (2M) {2821 ...
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