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winter 2004 2nd mt

# winter 2004 2nd mt - CHEM 14B" YOUR NAME Instructor Dr...

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Unformatted text preview: CHEM 14B '" YOUR; NAME Instructor: Dr. Laurence Lavelle WINTER 2004 2ND MIDTERM (Total number of pages = 7) (Total points = 50) (Total time = 50 mins) YOUR DISCUSSION SECTION .................................... .. YOUR TA is: Franklin Ow Sam Ho Carlos Hernandez Mo Chuautemoc Arellanes Write in pen. Show all your work. Check your units and significant figures. Think clearly. Good Luck. Constants and Formulas Planck constant, h = 6.63 x 10—34 J - s » Avogadro constant, NA = 6.02 x 1023 mol'1 Gas constant, R = 8.314 J.K‘1.mol'1 = 8.206 x 10'2 L.atm.K".mol'1 = 62.364 L.Torr.K'1.mol’1 Speed of light, 0 = 3.0 x 108 m.s’1 Faraday's constant, F = 96,485 C.mol‘1 Water, specific heat capacity =4.18 .J.°C".g'1 0°C=273.15K 1L=1drn3 iatm:10‘l.325 kPa 71:3.14 E=hv AE=q+w q=nCAT Wz—PXAV SszInW PV=nRT w=—V1IV2PdV = -nRTin% AS = 9% 1 ASTI T2 = Tiff? 99% = n c In £2 AGO = AH" — T A80 AGoz—RTIHK AG=AG°+RTIHQ AGO = - n I: E0 A125 0C, ECELL = E0 - 00:92 LOG Q d A 0.693 d A Tkﬁ = —kdt In [A]=-kt +ln [A10 t1,2=T Th; = kdt 1——i<i1 t-1 dA—kd A-kt A [A] - + [A10 1/2— [A]O [I— ‘ I [I" + [IO tugzLSJﬁ k:Aexp(:ﬁE-?) lnk=—%+lnA QlA. For the cell diagram Pt li~H2(g),H+(aq) Cu2+taq) Cu(s) Write the half—reaction that occurs at the anode? (3pt) H2(g) —> 2H+(aq) + 2e— 9711‘ away M‘W B. Given: Ag+(aq) + e— —> Ag(s) E° = 0.80 V Fe3+(aq) + e- —> Fe2+(aq) E° = 0.77 v Cu2+(aq) + 2e- —-> Cu(s) E" = 0.34 v Which is the strongest reducing agent? (3pt) (Note: Reducing agent is asked for, not reducing agents.) Cu C. Consider the following reaction: 2Ag+(aq) + Cu(s) —9 Cu2+(aq) + 2Ag(s) If the standard reduction potentials of Ag+ and Cu2+ are +0.80 V and +0.34 V , respectively, calculate the value of E0 for the given reaction. (4pt) 0 wt 2 A97ny 1% 3 1/43 {5) E U.) Q2. Balance the following equation, using oxidation and reduction half—reactions. The reaction occurs in a basic solution. Identify the oxidizing and reducing agent. (lOpt) Reaction of bromine in water: ’Br2(é) 9 BrO3‘(aq) + Br" (aq) 0 7"5’ ‘7 M) W: 51 M) + 2t“ —> 2 47%) QMW are) ——7 Maj-W) r/oe— gal) W @W 0 gnu/«d + {Map Maw/o; (W '44“ 0/4 W ﬂ 5/41) 7L M2 0%] f/Zbﬂay A? 25%}W)::Zﬁo£/ 06 Wu WWW {[ﬂ’rb/ﬂ) +Ze’/->Z&2ﬂwj 7L/Z "9 65%7M 7L/ﬂtdﬂ/ +/0€,_ tL/Z 5/1?“ ﬁ/ﬂg/ng +Z£a;/W) +5520“) ‘5' Z (M) 2 e w) + 4 W "e few be m ﬂea/La ﬁz4a/Zfﬂﬂ'" ‘ WWW” Q3A. Given: 4F62+(aq) + 02(ao) + 2H20(l) a 4Fe3+(aq) + 4OH—(aq) 2pt) and rate = k[Pe2+][OH-]2[02] What is the overall order of the reaction 4_ / What is the order with respect to 02 1__ /W B. If the rate of a reaction increases by a factor of 64 when the concentration of reactant increases by a factor of 4, the order of the reaction with respect to this reactant is ___3 (2pt) ¢fea¢ C. The concentration—time dependence for a first—order reaction is given below. 1 MI” Aloha: concentration of reactant. M! ——+ Qt > WNW Nummmw i Ullt’ —---) At which point on the curve is the reaction fastest? A (2pt) D. The concentration—time dependence is shown below for two first order reactions. Which reaction has the greatest t1/2? Clearly indicate your answer with an arrow to the upper or lower curve. (4pt) w“ A \ 'l’mn- -—> upper curve Q4A. For the reaction cyclopropane(g) propene(g) at 500°C, a plot of ln[cyclopropane] vs t gives a straight line with a slope of ~0.00067 5’1. What is the order of this reaction and what is the rate constant? first—order / 711‘ slope = —l< k: 6.7 x10-4 s—1 7, ﬂi’ v/M‘Uiﬂ MM B. For the reaction HO(g) + H2(g) a H20(g) + H(g) a plot of lnk versus 1/T gives a straight line with a slope equal to —5.1 x 103 K. What is the activation energy for the reaction? (4pt) (4P0 54 r K (Km/07%) = 5-3/4; I WM” (ﬁx/5% __ c; ’ / I >00 MAW 1%” E4 : ééz/trmﬂ C. Given: CH4(g) + Clg(g) —9 CH3Cl(g) + HCl(g) (2pt) The rate law for this elementary process is rate = 1<[CH4][C12l QSA. An elementary process has an activation energy of 40 kJ/mol. If the enthalpy change for the reaction is 30 kJ-mol"1, what is the activation energy for the reverse reaction? (Spt) awe/«r.w€'/ F 54 {7%}:gw’f0 agar”? 4H=30//<J.Mo{ / B. ’ Consider the following reaction: 2N20(g) —> 2N2(g) + 02(g) rate = k[N20] For an initial concentration of N20 of 0.50 M, calculate the concentration of N20 remaining after 2.0 min if k = 3.4 x 10-3 s-l. (Spt) 1.0% 3 /20/¢/“C ...
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