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CHEN1211Spring08Test3

CHEN1211Spring08Test3 - Adana<9 CHEN 1211 Midterm Exam 3...

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Unformatted text preview: Adana: (<9! CHEN 1211 Midterm Exam 3 Wednesday April 23, 2008 Instructor: Prof. Doug Gin This is a closed book exam. There should be a total of 11 pages to this exam booklet including the cover page, a list of constants and conversion factors / salt solubility table, 2 equations pages, and a copy of the Periodic Table. There are 17 questions in this exam worth a total of 100 pts. There are five 8 pt questions and twelve 5 pt questions. Answer all questions on the separate Scantron answer sheet by darkening in the proper bubble with a number 2 pencil. If you change your answer, be sure to thoroughly erase the undesired mark. Make sure to write and bubble in your name and SID number on your Scantron answer sheet. Read the questions carefully. Note the point value of each question and budget your time accordingly. Feel free to use the front and back of your exam booklet pages for scratch paper. The exam booklet is not to be handed in. Any answers not included on the Scantron answer sheet will not be counted. You have a maximum of 1.5 hours to complete this exam (7:30 — 9:00 PM) GOOD LUCK! By taking this exam, you agree to abide by the CU Boulder Honor Code for this test, as stated below: Honor Code Agreement: "On my honor as a University of Colorado at Boulder student, I have neither received nor given unauthorized assistance on this wor ." Additional restrictions: (1) Please turn off all cellular phones and other related wireless communication devices. The use of such communication devices is prohibited during the exam. (2) Calculators are allowed in this exam, but devices capable of storing more information, such as PDA's, laptop computers, etc., are not permitted. (3) The use of headphone audio devices capable of data storage such as MP3, CD, and cassette players are also not permitted during the exam. Any student found using such restricted devices during the exam will considered to be cheating and will be reported to the CU Boulder Honor Code Council for punitive action, as outlined in the class policies. (1) An irreversible one—step reaction has a rate constant of 10 3’1 at 300 K and 20 3‘1 at 400 K. What is the activation energy (Ea) of this reaction? (5 pts) . 2.3 kJ/mol (*3 z. (=f'z #275") 23:214.? . E #@ a (d) 19.7 kJ/mol " '4 ’ o __ (e) 4.6 kJ/mol (‘fi' ‘7!” mm»... .r.,. (2) The reversible one—step reaction shown below has an activation energy, Ea, for the forward reaction of 63.8 kJ/mol; and an equilibrium constant, as written, of 1.3 x 102 at 100 °C. What is the E, for the reverse reaction at this temperature? (5 pts) A4 K>>( so game m ‘ H025 PEAK 2A ‘2‘ B + C b... Locum. E. , (aq) P gm (317) C Q EQUlL. — us, axow K : £4 a, *e «Kr (e, am a) 15.1 kJ/mol z; e' 22* mac-east) b0) 78.9 kJ/mol __ + - .3 (c) 48.7 kJ/mol = e 1' F - [2‘3” XKO %b 33 gig/1‘2?" ‘Zn /< = *W " (373.695? ' ‘ 437' 1m (Asma‘ + RY’ZAK: “£91.?"th 63.ng { -= E... gun/(+5., EHA=C78- 9 Am (3) For the reversible reaction described in Question 2 above, which of the following statemen 3 IS TRUE if the temperature of the system is raised by 50 °C and equilibrium is re-established? (5 pts) (a) The rate of the forward reaction is now faster than that of the reverse reaction. (b) The activation energies of both the forward and reverse reactions change. (c) The value of the equilibrium constant remains the same but the system shifts more to the reactant side in terms of participant concentrations. (d) More products are present compared to before, and the value of the equilibrium constant increases. [253M More reactants are present compared to before, and the value of the 633 equilibrium constant decreases. Fog Exo’teemc Fbmfieb [2204 m EQDtL, PEUGEgS: 9A é €>+¢® WWW-was. »- ”an“ . If . i m “2‘ T. 234M @9832 W be“! é“ w A!» HOPE m...» m Email... W73 sass 54+ch 24L— m cFFefa-r' mereT" 2 C+ K Eschage$b (4) Which of the following statements is true for the reaction—energy diagram of the irreversible reaction shown below? (5 pts) 3 —~ {315? HFa-l a SEW—z. 3 AEEKN : C.) EXOfiWlC,_ Reaction Coordinate Step 1 has the smallest individual rate constant in the mechanism (b) The reaction has 3 reaction intermediates (c) The rate-determining step is step 2, and the reaction is endothermic overall (d) Step 3 has the smallest individual rate constant in the mechanism (6) The reaction has 2 transition states (5) Which of the following Br¢nsted-Lowry acids listed below would you expect to have the highest acid strength (i.e., the largest K3)? The proton that is lost in acid dissociation from these molecules is underlined for your reference. (5 pts) .153 ‘5'? [ 9 LOOK 9; Ba, amen-1W 6:- A9 913mm HA6¢$>+ Hp”) < “30%,;4 A5131; + FAmebgrmmuwm 9 can We ’0" ( // ° .. || ... “DEE (a) H3C—C\ ~ 0m»; (b) HzN-u -n @ H30—§—Q- 0 ma sm‘ «14440 mom a W u» ”.9 e) «.0- ii a W mm’ 5 ”L52 ' ”-9 fit; N» .‘?3 “T 5:, ,_., =3 EN ‘5 9 «roam- a -- ~ gas 1:— \l\\ f Form-(vs 5(9ch 90 0 (d) “30‘“ (MN 53-) $33: mo 9 a .. a Lh5 ‘ l' 2567 F0?- >6; C 0 new“. Frame 9 6!? re) . J (6) What is the pH of a solution at 25 °C prepared by mixing 211 mL of 0.500 M fisolutiorlufi‘l‘ ‘ with 189 mL of 0.250 M NaOH solution, given that Ka = 6.7 x 10—4 for HF? (8 pts) fibuos a 7.11 3.0 _ SC); 2.45; 6135 8EPW$1 3% $547" For? :30 L077 ON ((1) 5.80 (e) 9.81 #3 ,HPLEE? MRIW .1”, 7 ' - , -Mmrta_q,._sau >+0t 231, Lr' 33— 0.46001: , - _ - -. - - , -_ - ,- am ._ - 9- -w--- _ - _.,- - _ - A .3. ,, 13:33.9 :fi =3 gees,- M. £96---- , _ Z " W W W ' ZWZ. 5&5473’MW ; ' Z Z ‘ ‘ Z W Z W'WWWZWW - .3 -- -mogLM3 9499.. :3 0 .13M M mi , - - _. - ,-,-,,--.;.&Ee,.:- 9199,4241,” 1539}? ,NQZF +:; +4» £5. in. aw_-_¢.LL&t-4_ _ -- -0, (7) For the reaction below: 2H2<g> + 2N0<g) N2<g> + 2H20<g> the observed overall rate law for the reaction as written is: rate = k [NO]2 [H2]. Which of the following factors would affect the value of the overall rate constant (k)? (5 pts) I increasing the partial pressure of H2 and NO =5 DOE$ 1391‘ W65- A (II) changing the temperature :9 A W More 10 A; Ae‘e‘l/ III) usin an a ro riate reaction catal st g ppp yEOQ’T.wwEE$Eq55.AU-NLL (a) Ionly ”<50 Weaning Tb b Iand II = " gr 6:) II and 111 “'4' ’l e ( ) land III (e) 11 only (8) At 77 °C, the equilibrium constant for the reaction: 2 IBr (g) Br2 (g) + '2 (g) n Er” is Kp = 1.10 x 10—3. If 1.00 moles of IBr is initially placed in a 10.0 L sealed vessel at 77 P = -—\7‘ °C, the equilibrium partial pressure of IBr is closest to w ich of the values listed below? (5 1&0 ts) =« P5” ' PI, , — / to N0 ’ 3 = W KP “pigs-‘3 5th " * p ”‘0‘" (a 2.78 atm «- I ”"2373“ ((9) 2-69 am 9 15’“ "a: A BPacmTWECW * c 2.87 atm "AW WDWJ‘R ”WWW"? ‘ ‘ 0 (d) 3-00 atm Wet.w,+--ww* x +/< Aug-a . 4. ‘ «awawtwmwmnfl. . ~~M N :1- 2(6) 363 atm aw (9‘87 mom Q)m (gag-RV a?” :1: ‘5 K :: x Q 5.80%“, __ 6" [ QEUHMON @/<) 5? QU/w’fi) P Car/vex; .3. ><~ or Sam A a? . ' :1 ,I a ' , = . a Q 58” (9) Which of the following changes, if applied, will increase the number of moles of H1 in the system shown below? (5 pts) H2(g) + l2(g) = 45 AH = -9 kJ/mol W - atm—I343 {- ' exonq. A‘s. (ohm (a) increase V 1‘ (b) decreaseV ‘ ‘ DEW c increaseT Wat»: W {[5, decreaseT u.) 5*; B“! e) addacatalyst DRDPPQNe—r" g EQUIL. Wu" WA QUAD EGAN $06.0(Hépl Wiloxm 31:6. 934;: -— 574x — 5:74;.p4x WlalOX105§8 .339?_,( H43x+4x __ q.oéos Mo 3 -(,2é38’ lb 34-4-4110'3K3‘ = Lm~ n (10) Given the following reactions with their equilibrium constants at the same temperature: _ —35 2 N219) + 02 (g) 2 N20 (g) Kp - 1.2 x10 - 7 N2(g) + 2 02 (g) —'= 2 N02 (g) Kp = 1.7 X 10 1 2 N20 (9) + 3 02 (g) i 2 N204 (g) Kp = 1.6 X 106 the equilibrium constanth for the reaction 60kt, W is clos6 to which of the values l1sted below? 8 ts ft ( p ) I .. é . 33x10‘46 51093304 ‘3- 2.mN‘;/”6+;€f KP." ham: ‘5) 3.9XIO3 f _ / ..—; __L_._—--:—"§-"' is 39x10‘10 Q-NSO “:6 27'“; 30’3— Kp, (.3ch 3)@ (d) 39x W30 a —-= 35:90 / = mm" (c) 2.56x102 éf; @6" <- M " _ KP; C I ,» _/ 3E a~>0+ =8 4N0: (4’93“ Ker-KP; Km. 7‘; 3-3:"‘M’“”""” A. 3 no ‘ ‘= 5 “0 (11) Sodium bicarbonate (baking soda) decomposes at elevated temperatures, as shown in [email protected] reversible reaction below: 2 NaHC03 (s) ———‘ N82100:; (s) + H20 (9) + C02 (9) Kp = 0.23 @155 °C Starting with solid baking soda only, the partial pressure of C02 at equilibrium at 155 °C is closest to which of the values listed below? (5 pts) 0.48 atm K? = PH ,Q ‘ Fee , P1439 55’ Pfioa. I 0.23 atm 5 “fi_ "M'fi?!’ NW, (C) 1.0 atm +X 3: K malt.» $75th ( ‘ l (d) 0.048 atm _. .. o. 83 = X. (N RAM (e) 0.69 atm flwwswwm. _ . =5,” 3/ q 33 2 fl - . Y Fm; Al o Q: 42 M (12) For the sodium bicarbonate decomposition equilibrium described above, what is the value of Kc for the reaction at 155 °C? (5 pts) _ Ah An 9.: +2» : a .3 E?) 15129wa KP KLCRT) 2H“, ares FEM (C 1.4x 10—8 s K : KP FQmafi HECT- (d) 1.9 x 104 r s Q ”15> e 1.4 x 10'3 z 0 . a3 (13) Which of the following pairs of compounds would NOT be suitable for making an aqueous buffer system? (5 pts) (3) C6H5NH3+ and C6H5NH2 b HCN and CN- HNO3 and N03- 9 HMO 7. is A EH'UEDNC: Au}: 4““ ) CH3COOH and CH3COO— nggfi W mm A 30%, (e) H3P04 and H2P04‘ (1...? a»)? BAsE: 5.1me (mm Amt: +CDWBA$HE1> 5w“: .95 (01% use: 5» “3‘5"? Aw) (14) Benzoic acid (C6H5COOH) is a weak, monoprotic organic acid with Ka- — 6.5 x 10—5 at 25 °C. Given this information, what is the pH of a solution containing 0.350 M benzoic acid and 0.250 M sodium benzoate (C6H5COONa)? (5 pts) K 1+ 6611,5005 A ”6933?? H303 +1 caécoos (b 256 mu- a 35015 /~, ~ 0 c.350H ' .« . 4' >< +)< 4.04 W WWW... £52? 7.10 4C0 3557‘)“ i - (K) H (maso‘tx) H (a) 6.50 (e) 690 (EHflCCausaoil - [44:1 (@113qu l , ~ .gmo s(§.§sgl ' A . X = 0.55:0 3.? I X“) S H: ('6: ”1‘36? (K10 5): $0 (15) What 1s the pH change (Ap' g of KOH 1s added to a 2.00 L solution cOnsisting of X>> (61‘ 0.350 M benzoic acid (C6H5COOH, Ka = 6. 5 x 10—5) and 0.250 M sodium benzoate (C6H5COONa) at 25 °C, assuming that there 1s no volume change in the final solution? (8 111me pts) W- .. = $04 a (Kean 5.1m; “ 53 £95»: iiiiW Fume»; (c) —0..63 Q1490“: + £3£% chmeflb +5’;q :Cdgauee + 53% 450 44$“? 44>? (d) 4113 w“ 3350“ 03°94 1 0 95° M .1 6445]] ;. Ac 11.11;:— z‘fl— 4 68' (6) +0 24 ”Agfiém—owml "+% L "L 1_:’.<,....,.-..C..... 4:25, 13% 6:31!" 4‘. ° “‘1” 1.211,; %S @fi fits—KEN} (>911 ($31: 1.. HHI‘HN 1 w» Pam? Pl§+figéfijfiu as 5,, C“ :11 CHECK— oa: (o’WFIW—z a-l KSIO ”SH ASSKHPT' :043( no ) A? 0‘ W? H (16) The Ksp oft 6 salt nggz 1s 3.5 x 10‘18 in pure water at 25 °C. If solid Hg2C12 1s added to " 4168 a 2. 00 L aqueous solution that has 7. 31 g of NaCl already dissolved in it, what is the maximum number of moles of Hg“ (aq) ion that can be formed 1n this solution? (8 pts) 6 7 3i MACK («Mi Nag! Maia? 6.0 x 10'8 moles 3:0 30:— 4~+ng1 3.001... 2.2 x 10‘5 moles -—-.O 06.25 M (C) 8.6 x 10—: moles \H q/ lab ((1) 3.7 x10‘ moles ’31:) :% j?" (i ) +90 5 j (e) 7.5 X 10—9 moles ”A"? 3 fl °’5 3&6 (a? DI-fi‘“ 316.1533“ ‘” "€311 » W..- . 5 gm: ‘3 [email protected])<§>. (o. Mas-+15%} “ ' ' M20 °6>§+3>17R =4x>(o.069g)>‘ AsSUWNé 3K«°'°65€H) 041.115,, 2: ax ) - Ase-anew. on' .41 1 ”S-r =30 3x10 . = 3 gr t __ - - Haifa. ‘ ' X 420623555 ’ RENO 8M /= Xaflé’s‘ (11—0 Xto 3H (17) At 200 °C, ammonia gas (NH3 (3)) can spontaneously decompose in a reversible reaction to reform its starting materials, nitrogen gas (N2 (9) and hydrogen gas (H2 (3)), to some degree. Initially, there is no N2 (8) and H2 (g) present, and a partial pressure of NH3 (8) of 1.00 atm is introduced into a sealed vessel at 200 °C. If the partial pressure of N2 (g) at equilibrium at this temperature is found to be 0.10 atm, what is the equilibrium constant Kp for this reversible decomposition process at 200 °C? (8 pts) (a) igxig: t‘aNHmfi) Nam 4’ 3 H163) <§> 4:2:10-3 (“n—”Ll (mm ”6 ,Q’ l ., x 1.0 4b, , 7' afo-W) \ £12.! 0%? +,,—=:.£9.;19fl;> (e) 0.9 Barri/4 0,2021% ‘3 040m 0.303% l WWWM” \/$$ = amend? . (<P 3 ( RE”: l ”I; : awe-aw i ‘3.- W ,-MM ...
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