exam_answers_152C_Exam_2_Key_Version_B

exam_answers_152C_Exam_2_Key_Version_B - Kfv CHEMISTRY 152C...

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Unformatted text preview: Kfv CHEMISTRY 152C HOUR EXAM ll (Version B) Winter 2008 Wednesday, February 27, 2008 Name: TA Section: Student Number: TA Name: Score (page) 1 ‘ 2 GOOD LUCK! 3 Watch sig. figs and units! 4 5 Total '(x/100) I. CONCEPTUAL / SHORT ANSWER: Answer all questions (subtotal =52 pts) 4 1. (a) Give the sign (+ or -) of the cell voltage sand of AG for both an ( ) electrolytic cell and a galvanic cell. Galvanic: 8_+ AG_-' Electrolytic: 8 - AG_-/-_ (2) (b) (Circle correct) In a galvanic cell, the electrons move away from the (cathode@§d§) while in an electrolytic cell, the electrons move aWay from the, cathode). {3 2. (a) For the solution of the wave equation for the particle-in—a box, why is n=O ) not an allowed quantum number? 4",," /7 m; .0 ""6225: 5(2) :0 / om ' ’4 (tr/fir") cy V”, A45 ’5'.» "5 L,” ct" ' rage/c“ fizz/7V “I; Act, vlo (b) What happens to the spacing between energy levels AE = E(n)—E(n—1) as L (the length of the box) is reduced? ' A; «.11; I 5-; 57940117 zncr-earof. 3. Rearrange the equation for photo-electric effect to give an equation for the (y) velocity of the ejected electron (velect) as a function of the energy of the incoming photon (hv) and the work function of the metal (hvo) ;1 4711/1: é?” ~41; 'vz: /}M y : [é/l’v'méjl/L %) /§2_q k5y® (ab) 4.. For the chemical reaction A ——> B, give the appropriate conditions for (V) spontaneity as a function of temperature for each of the following cases (Possibilities: spon at all temperatures, becomes spont at higher temperature, becomes spont at lower temperature, never spont at any temp) (a) AS<0 and AH >0 Ari/WV; W’e/ 9/6”§’4"/’ (b) AS<0 and AH <0 5pm 9/ kw" 24”)” (c) AS>O and AH >0 gm! «#11’91” 24’? (d) AS>0 and AH. <0 2,6,1 9/ q// >427» 5. For the following values of AGO , give the corresponding values for the equilbrium constant K (K >1, or K<1 or K=1) ; If AG°=O, then K=? 1 () . If AG°>O, then K=? 41 If AG°<O, then K=? >1 6. In the rechargeable Ni-Cd battery, the redox reaction Cd (3) + Ni02(s) + ZHZO (I) --—-—> Ni(OH)2(s) + Cd (OH)2 .(s) ")7 : Z . (6) produces a standard cell voltage 8° = 1.50 volts. What is the maximum useful work wmax (in Joules) obtainable from this battery under standard conditions? Z a 7 A6: wan”: -m}€6 ;- — zmfiwjfic foihQ/ZYOW 1’ 52387114 16f} 7. Balance the following redox reaction, showing the separate oxidation and reduction half reactions, then the combined net redox reaction: (41 VO2+<aq> + H‘”<aq> +Zn<s) --i---> v02*(aq) + H20(|) + Zn2+(aq) xZ(V02++2//*/;~>V02f+ #20) M”0/A“/c‘fl) «4— 2+ L575 (62) + 4l/(iz) +§1467 v; QVOK *2/4404) + fi/GZ) “' K? C KKVQ’) @452 8. Next to each of the following founders of quantum theory, write the equation most associated with their name in this context: (4') Heisenberg MY) (AP) 3 2’72. » Schroedinger = f it De Broglie ) : % V Einstein (not E= hv, not E= mcz) % 9111/2: 4V ’A‘Vo’. V '9. How long will it take to plate out 4_._(l moles of Ag from aqueous Ag+ solution _ (5') with a current of 200.0 amps? ( Recall: amp = Coulomb/sec) - s ‘ CC ' 11,-sz Cquzc : .OM¢My Wsaygd‘o! éfé ’ i W” caym _ _. 4% r' N 141'mc (Sec) 3 (W93X/0 51C} or ‘0. {Vb/52 10. Consider the reaction: 02(9) 9 20 (g) . . + E? (if) (a) Predict the srgns of AH and A . (b) Would the reaction be more spontaneous at higher or lower temperature? 971 4; ,, 74,7, (2} 11. (a) In the Bohr model for the energy levels of the H atom, why is the sign of the energy negative? H/emre ext-’37 (5/1,) 5-6) rs a a mw/ wean Aw! we: 90 (Z) (b) How does the energy spacing between energy levels AE vary with increasing n? Af C/C[Wo;¢'} w; 23-» (Pear/3 47 S‘fhce “L 49’— ,\ \X ll. QUANTITATIVE: Do all four (4) of the following: (12 pts each) //2) 1. (a) Using the thermodynamic data given below, calculate AGO at 25 °C for the reaction, with all gases at 1.00 atm pressure: 2302(9) + 02(9) ----- ——> 2303(9) AG? (503) = - 355 kJ/mole AG? (302) = 5 285 kJ/mole AG 92cm 3 2 AG £505) 4%; (50%), My» 32035 (on ’- zcezgsu 3 ~— 0 LJ _ (b) Repeat the calculation for AG with all gases at 20.0 atm pressure. L Ara—[MW RT m o - V303 Q: a .1: RD _ NH”, was 1‘- ‘l47. 4 M {/2} 2. For the precipitation reaction Cu|(s) 9 Cu+(aq) + |'(aq), the solubility product for Cul (s) is KSp = 2.5 X1044. Using the reduction potential forthe half-reaction Cu+ +e' 9 Cu (e°=+0.43 V), calculate 8° forthe half-reaction: Cul + e' 9 Cu + l' (Ll/{I + Uggur I" £02? A9,”: «1356;. ? ~RTMK CM 7Ca+'i‘e-‘ 79°=—-o.+3v maze”: —r2~rlmc 50:“: 52m? " OASV 52f”: 12’:an ,0 _ ‘ W teal - 'O.80\f+ 0.434 ED _ _ Cg‘glfifiwwm(gamut:) Le“ I umuqem 45$.) Z 'O.S’OV _ A /§'Z__C. K5y@ (/2) ‘ 3. Chlorine dioxide (ClOz) is produced by the reaction: \ 2NaCl02(aq) + Cl2(g) -) 2002(9) + 2NaC|(aq) Using the following reduction potentials, calculate 8°, AG° and Keq for the production of 0'02 at 25 °c. CI2 + 2f?- 9 gCl‘ 8:: +1.45V Ea: 0M2V CIOz +e 9C|02 g : 0_824V A670: “’20 022+Za/fl7 260’ 50'; MSV ‘ Keg:— L‘l‘lfi/OZ‘ [9136714207443 ‘ ’~—*7 1‘ ' ' "°= -o.82,4 .- e : Lhcujii {F At]: 420000) 26002240“ €02M>~72mozcaqg+2com age“ 2 0,02ch - 4 AQ": ant'u“ ' I J = {zinM'XCllptgg’figu (Mung/qr I05,J) : ’lZOIg’ AC4”: ' RT MKeq’ -AC'i/ET Kai]: e t J. . 81¢) : ‘6- W " L4 q ( 12) 4. An electron in a one-dimensional box requires a wavelength A: 4642 nm to be excited from n=2 to n=4. Calculate the length L (in meters) of this box. «wwemfimwawmmwm t vmvaww'nwu:vrwwa-u _. u it i, ,, . . . i . A . i t ‘ A (ffcat;2;2= 104.3 m) I}: (hum/0&4 Egg 8’) (‘4M2xlo‘qm) a 1. 8/le PMHCM M max 3 (Ol./Oé’x/o'3’/<gr) (Zflqu/o W750 AtthZDSU— Y :l,(o8615wo’17m2 be .,. m2 k 2?le g L2: g—fictnf' n? ) l3: lkg'm} A " 41042 nm=4b4zqum ...
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exam_answers_152C_Exam_2_Key_Version_B - Kfv CHEMISTRY 152C...

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