10_CHM_31_Summer_Exam_1_Answsers

10_CHM_31_Summer_Exam_1_Answsers - Name w” CHM 31 First...

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Unformatted text preview: Name: w” CHM 31 First Hour Exam, Summer 2010 i’rofessor Roberts General instructions: Please label each page with your name. Read the instructions for each problem. Work those problems you know first, and then move on to those you are not certain about. Please note each problem has the number of points in parentheses; the entire exam consists of 120 points on 9 pages total (including this cover page). Time limit = 60 minutes. The multiple choice problems are graded only by the letter that is circled — if you change your mind, please make sure it is obvious which letter you intend as your answer. For the other problems, show your work in sufficient detail to demonstrate your mastery of the subject, but be brief if possible! For these problems only a small percentage of the total points are given for the actual answer — most of the points are in the setup and the process of determining the answer. If you must use the back of a page, please indicate clearly the flow of your work (label the problem number, such as 4C). Please write legibly so full credit may be granted for correct answers, and partial credit may be awarded for correct steps. This page may be torn off the exam — please make sure your name is on the remainder! R x 8.3145 J/(K*Inol) 2: 0.08206 L*atm/K*mol 1 L*Atm r:- 101.32J 4.184 J / K * g 2 specific heat capacity of liquid water (H200) ) Compound an; kJ / mol s0 J / moi K no; 10 / mol calm) —84.68 229.60 32.82 C(s) 0 5.740 0 om 0 205.138 0 com 393.509 213.74 394.350 Hzog} 241.818 188.825 428.572 H208) —285.830 69.91 —237.l29 Name: L CHM 31 First Hour Exam, Summer 2010 Professor Roberts 1. (36, points, 4 points each) Please circle the letter of the correct answer for each of the following problems. i) During a spontaneous chemical reaction, it is found that ASSys < 0. This means A. ASS“, < 0 B. AS,urr > 0 @ A853,, > 0 (and larger than |ASSys I) D. ASS“. < 0 (and larger than IASSys I) D. Cannot be determined from the info given 53;”. 7" 3%“! 1M, 5 A S; A/ i V Maw 13 + FM 4 SflM/Wffiolfi Pacer; ii) Order the following forces in the approximate order of increasing strength: .. S A. dispersion, ion—ion, ion—dipole, dipolewdipole, dipolednduced dipole HM] ”All I B. dipole-induced dipole, dispersion, dipoleadipole, ion—dipole, ion~ion L “if 2 C"'d'ld'1d'ld'l'ddd‘ld" D/Sflb/fl/l/ . ionwion,1on— 1 oe, 1 oeu 1 o e, 1 063—111 ace 1 o e, is ersion P l3 p P P P /S Wffl/‘I’E‘S‘T .dispersion, dipole-induced dipole, dipole—dipole, ion«dipole, ion~ion E. dipole—induced dipole, dipole—dipole, dispersion, ion-dipole, ion~ion iii) How many of the following processes would one predict to have a positive value for AS? steam < =2 > liquid water 43W - ,9 9/? Hag) + “20%) < H > H208) A “’4’ "" 8“ 91 Aggog, + 2:113:13, < m > 2AgBr{s) + H200) a ,4, .... '4’ l“ 3* 9"” Ag20(s} < =22 > 2Ag® + 1/202(g) Jflb “f' ,4, waif?” A.() @1 OZ 13.3 3.4 Name: Kb, i CHM 31 First Hour Exam, Summer 2010 Professor Roberts iv) When a system absorbs heat from the surroundings at constant temperature, the signs of q for the surroundings and Asmundmgs (look carefully — q and AS are for the surroundings) are: A. Both + g Both ~ C. q is +, Assurmmmgsis — D. q is -, Assgrmundgngs is + -q 1S +9 ASsurroundings 18 0 65. bM’WS Emma/VIEW“ => fiW/g w] Agm/fl .._.. V) Which of the following is the best solvent for making a solution of CC14(1)?/W/V~Pfld49€/ A. H200) Fab/12¢ B. (1&3on Marie, C. NH“) Maw @ Cfiném MOI/"ML/ffl/ E. Both A and 13/7 “ a w fl/SSW/WS 14% vi) Which of the following expressions preperly represents a 2nd order reaction with respect to the disappearance of species A? A.ln([A]t)x-kt + 1n([A A])/§" B [A] =[A10 — kt 077/ @[AL : [A]o/(1+[Aiokt) DIAL = [AioeXP(-k0 I” AL: i/([A])2 — kt/WWM‘ {w WWW Ta Rafi??? + 59¢]?ch 34]? WW my .05 MW we: M Mjfti’fi’flfi :? $379 4, At 3&6 77775 [5 2M fl/{flw Vii) At a certain time in the ieaction below the product 13 being formed at a rate of 0.10 moi/L 3. How fast is the F disa eating? 2(g} PP f Fug éj/Z A/fig/F (j) 2 N02(g) + F2(g) < :3: > 2 N02F{g) M? L Z {39: hwy/fl}? A. 0.10 moi/L's B. 0.20 Incl/L's (.0 050 moi/L s D. 0.30 moi/Ls E. Cannot be determined from the info given 3 Name: [L f} CHM 31 First Hour Exam, Summer 2010 Frofessor Roberts viii) Use the information given to calculate AH for the following reaction: 221103} “1" 28(5) < ==> ZZBSG) + 02(83 6/} x2, an Far/9 Zine} + 1/2 g) <=e> 250(3) AH e 348 kJ +676 £3? X2— H2<g> + So) <====> st® AH = ~21kJ “' tie/U XL 211(5) + {123%} <==> 2118(8) + Hug) AH = —185 kJ mm - 8' A, +142k5 +284kJ c. ~739k} ”L a “I D. 654 kJ E. —284 kJ ix) Which of the following ranks the listed compounds in the correct order from lowest to highest in terms of boiling point? A. C12, NH3, C24 50, CHfiI‘IQOH B. CIQHQZOH, CH4, HF, H2CO gr 3, . MS 5' g 3 X C- C232,, NaCl, H20, Cfgs ,- Hz: NH3, H 0: C12H22011 s .6 ~ g 3/ f 5’ E. None of these shows the correct order F. All of these show the correct order. #20“) ._./ 3M3, NEE/K .... mar/W pew/gases 1’7: C12; #62 (pl/{5) 51” “KM Z 3 €77,615: gfl/é/fl/Ci Name: g I CHM 31 First Hour Exam, Summer 2010 Professor Roberts 2. (20) ThermodynaIinc data for this problem are on the cover page. A. Write the balanced reaction for burning of ethane (C2H5(g)) with pure oxygen (02(9) to form carbon dioxide and water. Assume all reactants and products are in the gaseous state. C3 Hg (5) ‘f' %@363) P5 ZCWafg) +3 flay/j) E. Find AGO per mole of ethane for this reaction. Work space: FM, [ST/eéflflflll/ A6}? 53%? Aéfp/Wdaofi w éflaz’fif‘fwfcy‘m 2F”, E Z $60”an ”f 3 56;”ch "" Mia/t2 (j) W '27-” @7363) “'5 20237.3, m We) #0233957? Wit) "' [flaw/Mew) “éfiWW v .... I) WM? H @ “fir, iii/MU“ c. Find Kequiabflum for this reaction at standard conditions. 5, M" WWW/by; M fife AW C SE K w 6+6 MW ar/Maa)/(mq5’37aa “Héfli’vt’YflMU/MM :r) «6; " @617 8+5’5ia5‘3 WML (2’ W +2521) D. Will Kequfl‘lbrium increase or decrease if the temperature is changed from. standard conditions to 350 K? Justify your response. Justification: A c; e; A H - f‘fiS I A f? /S w TWflM/fimf way/’WflW A; in 2/314) +3 085,353”) ___ ( 33‘1””) - gpmizia fig, A5 2: t/észya ire Sigma—7:45 ‘I may: ma Name: ___K€Y.*__.___ CHM 31 First Hour Exam, Summer 2010 Professor Roberts 3. (16 points) The following parts are related to each other. A. Given the following data, determine the rate law for the reaction Nwaq) + NOW) < me > Nag) + 2Hzoa} Experiment [N H4+(3q) ] (M) [Nozyam] (M) Rate (NUS) 1 0.2501xl)d[0.250 [1.255(10: ”IX; 2 0. 500 0250 «rt 2 50 x 10 3 3 0.250 X2, 0.125 7’ 6.25 x 10 Work Space: ‘ HZ; mmcfi’ffl/I’fqgalj 2 RateLaW M7? 314 MM]/”%] M573: MUMB 5/91” edge M/ [Wt/me] was Harra[fi/r2w])2flr Mme y/Jam W W 74a] B. What is the overall order of the reaction? OVerall reaction order = a 5ch are/17m: /H 1‘2, C Calculate the value of k in the rate law for this reaction. Work Sp ace: Will/”wellmm] — 3 l "M [ 251w f, er 4 > ’5 [WWLr/Wzmfl Myanmar) Sat/5&5 M 5 “I MAJ/75 We M779 W»; HA 3(éflfl/5)CM)OVI) j) 5,me w x7 5 D. Is it possible that this reaction could proceed via an elementary reaction (i. e. does the reaction mechanism have only one reaction that is identical to the overall reaction)? Circle one: No Wax/44 5 ké‘of’wfi' Ext??? MW 2: (Mr/5W WW 7%? ma m emcee ream/J We 0 W46? am are. Edema/77M ,V flt’flC’W/J , I Name: —————--«—l——-————-— CHM 31 First Hour Exam, Summer 2010 Professor Roberts 4. (l6 points) An “I can fix it myself” friend asks you to help him mix antifreeze for his car. He knows his car will hold 5 gallons of liquid, and he wants to move to New Hampshire, so he wants protection down to ~35 DC. He asks you to help him calculate the relative amounts of H200) and ethylene glycol (HOCHQCHQOHO}, molecular weight 6207 g/rnol) to make enough antifreeze solution to fill his cooling system, and he doesn’t care if there is too much. He has already purchased 4.0 gallons of ethylene glycol. Some useful information for this problem: 1 gallon m: 4 quarts z 4 liters (for this problem, at least); 1.00 g H200) : 1.00 mL H206) ; density of ethylene glycol = l.ll g/mL; Kffor water = —l .86 0Chen; Kb for water = 0.52 0Chan. A. What concentration of ethylene glycol in water is needed to protect the coolant from freezin down 0 ~35 0C? nswer. Work siace: tfir: [470% A I, 05—45% flflfl L 66,6794) ”35’ C ”HIM/WWW -t> X r 2% ~ lat/my S’ M Men/5 Mild/fl, : # W Worm A; seams/7’ (few (1,... ) ”’51 Wang HMS EWVW Gil/w; ., (/8?! MM) )(fiyyflfldw mg L) (item; .2»; are we“ L ran/W mm, w W L Wm; 13. Just for curiosity, he also wants to know the boiling point of the solution. What is it? Work space: T :- K W Answer: :- ” ‘7 A E ‘9 a SMZWM/ ”(l/5' 5* ' f 475 WJVC/Mf/E'XM 3-“: W73 “’0 (r are) ram/M6 WW 2: Er W + A 72 :- W +25 =: mg g C. The actual pressure in the radiator is much higher than atmospheric pressure. Will the boiling point of the mixture at the higher pressure be higher or lower than the value calculated in part B? Circle your answer, but provide some additional information to illustrate why you $852316; 00??ng Lower B. l). ; " '- 5,9,, "M WW WW“ "' m w ”””” MW ’23 lawyaflfira QW/fi F S - MW 0W Name: EV CHM 31 First Hour Exam, Summer 2010 Professor Roberts 5. (16 points total) The following two parts are unrelated to each other. A. A rough reaction profile for the oxidation of (30%;) to COM} by molecular oxygen (026;) ) on a solid catalyst such as an automobile catalytic converter is shown below. In one sentence each, describe what molecular species are most likely present at each of the lettered points ~— indicating chemical species by formala might help. eac 1011 oor mate PointA: €065) ‘f’gaffl f/l/ Giff fflfiwwg M W73 . a w— . w... ,6 0/0/ PomtB; C0571, StflW+ g.” JdAFM MMM/AWW é/W’ fa£f4i% PointC: 0 wanna mew/mm oer/ff? ifwflw 5/729: PointD: CW3 WV SCI/(«FM M fif/ffly W/q/ figSflMWfl/V PointE: 002(5) e... we: PMflU/Dr B. Fill in the table below (6 entries total): AHO AS0 Temgerature Soontaneous? 6 0’ ,4, '4 ' - a A 1 S‘ __ F” + “f’ W67H Yes SMfl/Wfims _ + Low Y6?) [ON 063‘)? l ,. WW Yes fl A6” 5 AW w 7273:” + + 09,4, *- Low No \ f raw/GWW 8 paw/4W0? Name: KEY CHM 31 First Hour Exam, Summer 2010 Professor Roberts 6. (16 points total) The following parts are unrelated to each other. For the first part, circle the letter of the best answer. i.) In the process of dialysis, a special semipermeable membrane allows both small molecules and water to pass through, but not large protein molecules. These membranes are used to separate these small molecules and ions from the much larger proteins. If a mixture of proteins and small molecules were separated from pure water by a dialysis membrane as shown below, which way would the water and small molecules flow? A. Both water and small molecules would leave the solution and enter the pure water. B. Only the proteins would move into the pure water. Water would enter the solution while small molecules would pass into the pure water. D. Only small molecules would leave the solution; water would not flow. E. Nothing would pass through the membrane. ii) Write down the Arrhenius equation and define all terms in the equation. in one or two ' sentences, describe why this equation is important. #17?) l1 ="— 4 e ”5%?“ an? pate/x75 M at 4% WNWWM 67F MWWW , 0W Ham/ea firm/W TM are as [M a) t W/ MM Mae/07’ W WM”? 7’ iii) Some salts are very soluble in water (i.e. NaCl(,)) while others are essentially insoluble (Le. Ag28(s)). Using a “Hess’s Law” type diagram with appropriate labels. for the various steps, describe why this observation might be true (according to what you’ve learned in CHM 31). man/W Maw; W W WWW y} . (75W 727% J? W754i“ MA WWW War/fix rF War WWV 5 7n Mr (M mew WWW: W mm 22%” We mm MW 05" ...
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