Practice Final Answers 2005

Practice Final Answers 2005 - Chem 1B White Version Final...

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Unformatted text preview: Chem. 1B White Version Final 2005 1. Using the following data: AG? (kJ /mol) N2H4 (I) 149 N02 (1;) 52 H20 (1) — 237 02 (g) 0 a) (6 pts) Calculate AGo for the following reaction at 298 K: Nzl-li (I) + 3 01 (g) —> 2 N02 (g) + 2 H20 (I). “(‘7 0 5 Z ' Z 3 ii [360: [’ZISZ)+2(»737)] - f1..th \béarr517k38 smolsm —> QW‘C‘l 90‘s b) (6 pts) Predict the sign of AS and AH. Circle the answer, 2) b 5 < O I'As<ol AS>0 AS=0 AG: AH_TAS EAH<0 I AH>0 AH=0 3:th in Mam/htlc c) (3 pts) Will the reaction be more spontaneous at higher or lower temperature? Circle the answer. Higher T Lower T S (8 pts) The standard enthalpy of combustion of 1 mol of ethanol, CH3CHZOH (I), is 71368 k] at 298 K. Given the following enthalpies of formation, calculate AH;o for CH3CH20H (I) AHf" (kJ /mol) H00) A235 _ CH 0H 4 0 ( __ 0 C202(g) #394 CH3 1 [) f3 2 9) > QC & 1. 3HZO AH: [2(«3qu)+ 302353” A z "363!”— x : #275 "47M! 3 H; (CHJCHZOHJ : — .27 5’ i‘T/woi 3. (6 pts) Write the reactions that correspond to the following enthalpy changes: 3) AH? for solid iron(III)oxide. , 3 7 .2 F515) 1- 201(9) ~—> F6103“) b) AHf" for calcium carbonate, CaC03. Cats) t CH) t Z702 (.9) -—> C0100; (5) Chem. 1B White Version Final 2005 4. (4 pts) Write the electronic configuration and indicate the number of unpaired electrons for each of the following species. electronic configuration number of unpaired electrons a)s [MeJSSZBPq '9 b) Se’ [9r] HSZJquPS l ikill. Mini 21) (6 pts) Draw the Lewis structures, all three resonance forms, for the cyanate ion, NCO’, assign formal charges to all atoms. Carbon is the central atom. “mam: =N-CEO= "” I, \ n + 0 ~| 0 a —z 0 ' b) (4 pts) Based on the formal charges, which resonance structure is least favored? N V C E 0 (6 pts) Draw the Lewis stnicture for each of the following molecules . SClz :Clos—CI: o; :ié‘. NZFA .. i “ ". :F-N—M-E- 0: ../ .. '- t ,F 1 F.‘ ' . t 7. (16 pts) Circle the formula that best fits each of the following descriptions: a) smallest radius 0‘ 0' b) largest ionic radius c) most polar bond longest bond length greatest electronegativity smallest first ionization energy P Cl contains the longest oxygen-oxygen bond length 01 03 an excited state electron configuration [Ar]4sz3d3 1522512194 ‘ [Ar]4sz3d64pl C—é: Clacl’ orientation is V‘oi’ [mpar i“ for Lew {S sfimcimres Chem. 1B White Version Chem. 1B White Version Final 2005 8. (4 pts) At constant pressure, the following reaction is exothermic 2 N02 (g) —) NZO‘ (g) 12. (6 pts) One mole of an ideal gas is heated fi'om 25“C to 35°C under two different conditions. First, the gas is . . . . . heated from 25°C to 35°C at constant volume then the gas is heated from 25°C to 35°C at constant pressure. In the direction written, the reaction is _ a What is the heat absorbed at constant volume, , relative to the heat absorbed at constant ress e, ? C' 1 th a) always spontaneous. A G - A H — T A 5 ) qv 1! ur q}, “'0 e e , answer. I b) spontaneous at low temperatures] V? E qv<qp l q = q q > c) spontaneous at high temperatures V P V q? b) What is the change in enthalpy relative to the change in energy lor these piocesses? Ci! cle the answer. d) never spontaneous. AH ; AE > AE s AH < AB 9. (4 pts) For which of the following processes would AS” be expected to be most positive? . Consider the following reaction mechanism: a) 4 C102 (9 —> 2 C120 (g) + 3 02(g) b) H20 (1) ~> H20 (5) A h g cm ‘5) N"Ha (g) + HCl (3) —> NHACi (g) d) N204 (g) —> 2 N02 (g) I a) (2 pts) What is the overall reaction? ! e) 2N205(g)—>4N02(g)+02(g)l Q _> 5Wal gov) 903 5 3 01 b) (8 pts) Derive the rate law. Be sure to eliminate intermediates from your answer. 03 r O; + O (fastequilibrium) O + 03 —) 20; (slow) 10. (4 pts) How many electrons are transferred in the following reaction? 3 . 0 6Ag + 3 HS’ +2Cr0f + snzoe> 3 AgIS + 2Cr(OH)3 + 70H : COL] l: /\ 3 J. g 669% 3H9;S+ 68' ll. (10 pts) Answer the following question using the data given below: Half Reaction if (V) 2* _ C0 + 2 e —> C0 (5) ‘0-23 c) (4 pts) If the concentration of 02 is doubled, while the concentration of O; is kept constant, how Niz’ + 2 e’ —> Ni (5) A023 will this affect the rate of reaction? rail A piece ofcobalt is placed in 0.15 M Ni(NOa)z. Calculate the concentrations ofCoz’ and Ni” at equilibrium, at 25°C. rm +¢ 04 66 r em w Jg ‘% {a} C 0 r .3— C0 m—av Co”+ze- E“: +0.8‘KV N.‘“+ 23' a Mits) ~0.23v (8 pts) In a common car battery, six identical cells each carry out flie following reaction. Pb (s) + Pbo2 + Hso; + 2 H‘ —> 2 PbSOi + 2 H20 5‘ = 2.04 V C 0 1, N " a + C 1 r ‘r N 1' ’i" 0 a 0 5 V Suppose that to start a car on a cold morning, 125 A is drawn for 15.0 seconds from this cell. How many ; 0 grams of Pb (5) would be consumed? "W‘Wl 0.5M 0 EanF/ET K26 g.— [Wolf'j IwclPla 207.83 ’ (0.053;)(amole‘s)(¢76485§“) \5.0566(l155a)(Vaijc)('-—’waie‘5)( Mal _ 1.9.043! (8.3lLlSr/wall‘)(zq31¢) M eiw‘i-b- 0.5-x l<:c WWI" ma Witwa— (47.1 0,1‘47 I"! : [Cold [Nil'j:0.i$~x: avast/l Chemr 1B White Version Final 2005 Chem. 1B White Version Final 2005 15. The molecular formula for ozone is 03. We can draw two possible Lewis structures that satisfy the octet rule, 17. (10 pts) Use the bond energies given to predict AH for the combustion of ethanol. a) (2 pts) Show all the valence electrons in the following Lewis structures for ozone '7 1"] If] “O’— H—(|3A(|3707H + 302 —> 2co2 + 3H20 ./ \ r H H . ‘0—03 0 Break Bonds ’1 “ ' Bond Ener J/mol -:> + 358 b) (3 pts) Which structure, if any, is favored (more stable, lower energy)? Circle the answer. 799 347 i. Both are equally favored. ii. The cyclic structure is favored. iii, The bent structure is favored. 495 F0 r W. 3 a W at S t 413 __ 463 :9 16. The rate of the reaction, NO2 (g) + C0 (g) —> NO (g) + C02 (g) depends only on the concentration of nitrogen dioxide at 200“C. The following data were collected at 200°C. _ I 2 5 6 k T/wa ' rima<min) [N021 (moi/L) ‘ DH ; - .Q 5 e tar/Wt 0 0.500 20 0.444 18. The figure below represents part of the emission spectrum for a one»electron ion in the gas phase. All the lines 50 0.381 Mg k f N 03 1 result fiom electronic transitions from excited states to the n = 3 state. 75 0.340 F A B 5—): vs 5 150 0.250 59 hat/"Emu?" ‘4 300 0.174 P“, blew: Wavelength—D (fin IQ WWW/Vb“ ‘3‘ a) (10 pts) If the reaction is second order with respect to nitrogen dioxide, determine the value of the rate emsmt at Lh‘s temperame' Be Sure to mdude “mm a) (6 pts) What electronic transitions correspond to lines A and B? : kl? + LineA: n:7 —-> “=3 0 LineB: “:6 -—> m=3 k- : 5 [a p e Z 201— b) (10 pts) lfthe wavelength of line B is 121.6 nm, calculate the wavelength ofA, X "7 V — Lineg F04 A : lQl,6 V'IVVI (6.6561(10'3” 35H swung W/S) huéluzrhm q away“ :2 .- 0t” ZIIXlfl‘ ’] s r MAO -49 —- 1.601 )tto’mj: . 2. I8Xla b) (4 pts) Calculate the concentration of nitrogen dioxide, [N02], afier 450.0 minutes. — 3 F) Li ’L‘ " L .9— I‘Ifl ’“L [H] — (amz (chW.h)(qsavM ) Jr 0'5“ - J— - 7.63 M Jr [Pd [a] = 0.13 M ...
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Practice Final Answers 2005 - Chem 1B White Version Final...

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