Midterm 2 key

Midterm 2 key - CHEM 14B YOUR NAME lnstructor: Dr. Laurence...

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Unformatted text preview: CHEM 14B YOUR NAME lnstructor: Dr. Laurence Lavelle WINTER 2002 2ND MIDTERM (Total number of pages = 7) (Total points = 50) (Total time = 50 mins) YOUR DISCUSSION SECTION ............... ... ................ YOUR TA IS: Andrew Clark Carlos Hernandez Franklin Ow Write in pen. Show all your work. Check your units and significant figures. Think Clearly. Good Luck. Constants and Formulas Planck constant, n = 6.63 x 10‘34 J - s Avogadro constant, NA = 6.02 x 1023 mol'1 Gas constant, R = 8.314 J.K“.mol'1 = 8.206 x 10'2 L.atm.K‘1.mol'1 = 62.364 L.Torr.K“.mol'1 Speed of light, 0 = 3.0 x 108 m.s‘1 Faraday's constant, F = 96,485 C.mol‘1 0°C =273.15 K 1L=1dm3 1atm = 101.325 kPa n=3.14 E=hv AE=q+w q =nCAT W=-PxAV S=kBan PV=nRT w=-V1IV2PdV = -nRTln\—\;f 0 AS = 94351 2 djflfil :2 o o AST1.-.>T2 =T1F T = nCln T1 AG =AH -TAS° AG°=-RTInK AG=AG°+RTan AG°=fn FE° At 25 °c, Ecm: E°- 00:92 LOGQ d‘A ‘ 0.693 fill = -k dt In [A]=-kt +In [A10 t1/Z=T d[A] = -kdt [A] = -kt + [A]o t1,2 = %% k=Aexp(§-fi) lnk=--§%+lnA Q1. Consider the galvanic cell based on the following half-reactions: Au3+(aq) + 3e- —> Au(s) E° = 1.50 v Tl+(aq) + e- 9 T|(s) E° = -O.34 V A) Determine the overall cell reaction and calculate E°(cell). (Spt) I ‘ M7517) +9372 Mk) 5‘: /.§0V (We) Zr 5 +9 fut 1+ 5’ “WW if}qu )+3’T/€@‘)’?AI4{5) +ZTJW) EM=l-8¢V' (M) to? ('_ a .m B) Calculate AG° and K for the cell reaction at 25 °C. (4pt) _l a 4: :- "hFE/‘ZJL : -— QM {X74 (gaffe. Mé)[/. MIC) ‘ (wt) ~522573€z H H (We) - 5’. 3'3 x/05T (4-9114) 44-3 “MA/r r: E”: “:1”sz 17%: ' c 30.13“ -.— 43.2543? h E ovofl’b 0. o {14' H k: M732"? 2‘ Lawn/’32 {MM 0) Calculate E(ce|l) at 25 °c when [Au3+] = 1.0 x10'2 M and [Tl+] = 1.0 x10' M. (3pt) MZfaC) M: a-ofqi 14 1 " ’ ‘ +3, ‘ 0 05’2 (LOX/0.“? 1Q: : /.X¢ —- ‘ 1 ) 3’ 6W”) ' 2 1' 3‘" 0'2511 (apex/:9) r.$§z~(—-o.177—3) ‘ (M) : 2:04; r/ €0.ffl%) ll Q2. Write cathode and anode half-reactions, the balanced equation for the cell reaction, and the cell diagram for the following reactions: (No calculations required.) A) Ni2+(aq) + Zn(s) —> Ni(s) + Zn2+(aq) (5pt) QM) may) tug: e; 14(5) W QM) 311(5) —>» 3’1"le *3/15 M QM) [1744/] +%a(s)——>,V4‘(J)f 6&2”) «tam. B) ci2<g> + H2<g> e HCllaq) (Stat) M QML] 42(1) 144?) a Z MW “Zn/WI /# m 4b. @i/fl‘ei/W/ Q3. The reaction l' (aq) + OCl' (aq) —> lO' (aq), + Cl' (aq) is believed to occur by the following mechanism: k1 OCl' + H20 == HOCl + OH' Fast equilibrium. (Also note that water is in large k-1 excess for this aqueous reaction so its concentration cannot effect the rate.) k2 l' + HOCl 9 HOl +Cl' Slow. k3 HOI +OH' 9 H20 + IO' Fast. Write the rate law for this reaction. . (1 Opt) Q4. The activation energy for the reaction H2(9) + |2(g) -> 2Hllg) is 167 k.J.mo|'1 and AE for the reaction is 28 kJ.moI“. What is the activation energy for the decomposition of Hi ? (7pt) (Hint: This is a simple calculation and you may want to draw a diagram to help solve the problem.) activation energy for the decomposition of HI = 167 — 28 = 139 kJ.mol'1 7pt incorrect sign -1 pt incorrect units -1 pt 05. Use the reaction A ---- --> P to answerthe following questions. (13pt) A) State the 2"d order differential rate law equation. (2pt) - £5? = k [A]2 (2ND ORDER DIFFERENTIAL RATE LAW) B) Derive (showing all steps) the 2nd order integrated rate law equation. (4pt) d A 4d? = k [At 915; * - [A] = k dt (SEPARATE VARIABLES) 1pt [71-] = kt + b (INTEGRATE) 1pt 1 AT t—O [A10 = b 1 1 = R [A] kt + [A10 (2ND ORDER INTEG ATED RATE LAW) 1pt C) State how you would analyze kinetic data ( [A] vs t) obtained from this reaction to test if the reaction is 2"d order and to determine that rate constant k. ' (4pt) PLOT fi VS t IF STRAIGHT LINE FIT TO DATA THEN 2ND ORDER RXN 2pt SLOPE = k 2pt , D) Derive (showing all steps) the half-life equation for this 2nd order reaction. (3pt) 1 1 1 1 1 2IAIo = “"2 + [A10 19‘ L 1 [A]O = k It1/2 OR t1/2 = k [A10 1pt ...
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This test prep was uploaded on 04/03/2008 for the course CHEM 14B taught by Professor Lavelle during the Winter '01 term at UCLA.

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Midterm 2 key - CHEM 14B YOUR NAME lnstructor: Dr. Laurence...

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