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105bf07_sample_e3

105bf07_sample_e3 - )CMDQJ Z 003 Chemistry lOSbL First...

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Unformatted text preview: ()CMDQJ Z 003 Chemistry lOSbL First Letter of PLEASE PRINT YOUR NAME IN BLOCK LETTERS 11:00 a.m. Section Last Name Fall 2004 Name: EXAM #3 October 26, 2004 Last 4 Digits SID #: Professor Arieh Warshel Lab T.A.'s Name: Lab Day and Time: Please Sign Below: I certify that I have observed all the rules of Academic Integrity while taking this examination. Signature INSTRUCTIONS: 1. There are 5 problems on 10 pages in this exam. Please check to see that you have a complete exam. 2. Please show all of your work to receive full credit. 3. You must use ink. Do not use a pencil. Useful Physical Constants and Equations: Avogadro‘s number N = 6.022 x 1013 mol" Universal gas constant R = 0.08206 L atm K“ rnol'l = 8.314 I K" mol" Faraday's constant F = 96,485 C mol'l K p = K C(RT)” Ea I Ink:T ;] + lnA —b:|: b1—4 Ifax2+bx+c=0 thenx=—2a—ac— PV=nRT. -w=q§ AS=k In W 136:-an AG=AG° + RTan AG =AH—TAS E=q+w AG” = —RT 111K“, 1. (20 points) A buffer solution contains 0.10 M of HF and 0.20 MNaF (here we refer to the initial concentration before equilibration). The K_ of HF is 3.5x10“. \5 .. a) Calculate the pH ofthis solution. P 13* = 7&7 (5- 5V0? [F-J 1‘ 3' 5‘4 79H 3' Pkg, 4— 1Z9? 10 b) 50 mL solution ofO. 10 M HCl has been mixed with 10 mL of 0.20 M NaOH. What is the pH of the resulting solution? ya 4~ Neal? --9 Mac! + #,0 95533 m .] 2.0»? '3 MI m —---——'.—r ¢ “ 3.0mm mu! +3 = Egg—1" = 0.050 ’1 [H " 5mm;3 L PH: 130310050)?” ['30 2. 0 (continued) A reaction that gives off heat under conditions of constant volume has: i) AE° > 0 ii AB” = 0 ® AB” < 0 1v AH" > 0 v AH°= 0 AH°< 0 g) The third law of thermodynamics states that: i) AE = q - w ii) AH = AE + paw iii) AG = AH — TAS @ S=Oat0”'K v) none of the above h) If W is the number of ways of arranging objects in space, the entropy S is: i) not related to W ii) proportional to W @ proportional to in W (or log W) w) proportional to e‘" (or 10‘") v) proportional only to the Boltzmann constant k i) For the reaction, '2 H.z + I2 = 2H1, the quantity [ Circle the correct answer. True or [Hzlllrl is always equal to the equtlibrtum constant, 2. (20 points) Circle the correct answers. a) A spontaneous reaction is one in which: i) AH” < 0 ii) AH° = 0 iii AH" > 0 AG” < 0 v AG“ = 0 vi) AG“ > 0 b) A reaction that causes the system to become cooler as it proceeds has: i) AH" < 0 ii AH” = 0 fl, AH" > 0 IV) AG° < 0 v) AG° = 0 vi) AG" > o c) At equilibrium, AG' ._. $6,. " 7L K735” Q i AG < 0 _ 0 ii AG=O ) dM 0: 06' +RTAK iii) AG > o (y' m mm M75 04": firemen}: v) AG° = o 1" vi) AG” > 0 d) The freezing of water is a process in which: i) AS° > 0 ii) AS°=0 [-53 Man Wm M67? AS°<O e) The reaction of PCls(g) —> PC13(g) + Cll(g) has: 6) AS°>0 lM9JZ/JM3 ii) AS° = o m) 4M“ M“ and-5w" . 3. (20 points) Given the following information: W5 (5) :3 Mn‘2 (aq) + 5'2 (aq) K”, = 1.4 x 10‘” ZnS (s) r: Zn"2 (aq) + S'2(aq) K.,, = 1.2 x 10.23 Answer the following questions: a) What will be the solubility of ZnS in pure water? ZnS 3-; gr!” +8;- )6 K (”‘IfS 0,6 ”07L (bid/M here.) K9,): XL =/LX/a 13M;- X -.:: 5.5)00 Iz—M .—I-' b) Which ion (Mn+2 or Zn”) will precipitate first by adding 5" to a solution mixture of 0.040 M Mn+2 and 0.0010 M Zn”? Show your work. [MSW—c“ Mn1++5r £7,31- £72+ _ k3 = I 1"” 3 2"” 8‘2 ’4' "1+- 2 P kf‘f: I'M-I -- riM JIS J I. Z”... ._=23 (0 “”‘QCIJ than {(5.0%) 3 __ [*7 575’ :C’V-J [32’] ”4’0” 3 : . )(l 4&4 [3 J15 Wat/é 4.92,,“ W5 AIM. “W )I 1‘ F\ [*1 7' .- A- no. .1 l... 5. (20 points) Consider the X10) —> X?(g) vaporization process. For this process AS“ = 105.0 J/K mol, AH" = 22.0 kJ/mol. a) What is the boiling temperature of M2 at 1 atm? a5! . 0 Moi»? 7— : ms)!“ M" 5. J/OK b) What will be the sign of AG for boiling of X2 at 50°K and what does it tell us about the direction of the vaporization rocess'? AG: 2-?)00 233— (SOHC’OSJZKWJ) Ad: Ma, 7572 3M4 : /é.82é,J'/nu/" c) What is the equilibrium constant for the vaporization process at the boiling temperature? . ...- _,.-‘. 1355—: pawn/2' = 0 we aflwmm ink =0 K =/ d) What does the positive value of AS” tells us about the relative order of the system? (Explain) X147) is ”MY?! a/x'sMrtl Vzém, {1&3}. 04> X2. (2) /‘5 1470?. draélwl flaw rill/f) or) X21?) f5 mm rm “MM Yaw. ...
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