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key1 - CHEM 31 EXAM 1 FALL 2010 NANIE HE i This exam must...

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Unformatted text preview: CHEM. 31 EXAM 1 FALL 2010 NANIE: HE i This exam must be completed without the aid of books, notes or colleagues. You may use a non- programmable calculator; if your calculator is programmable, you must present it to a TA and have it cleared before you begin the exam. All answers must be clearly written in the Space indicated and mathematical work must be shown for full credit to be awarded for numerical answers and for all answers for which calculations are carried out. Please write your name on the top of each page. A periodic chart is included as the last page of the exam. GRADING: (Page): Total Total points points awarded ossible (6): (7): 14 J (8): 17 I (9): 10 "(rlg)iAL?100 L l J Good luck, and remember: The most exciting phrase to hear in science, the one that heralds the most discoveries, is not "Eureka!" (1 found it!) but "That's funny..." ~Isaac Asimov NAME: if“? 9 Circle the letter of the correct answer or write the answer in the space provided. If numerical work is required, show it in the space provided. Points are shown for each problem. 1. (4 points) Which of the following ranks the compounds from lowest to highest in terms of boiling point? (a) C12, NH3, C60, CH3CH20H (b) C12H22011, CH4, HF, H2CO (c) Csz, NaCI, H20. 01ng @ H2, NH3, H20, C12H22011 (e) none of these shows the correct order. (f) all show the correct order 2. (4 points) In each of the following pairs of compounds, circle the formula of the one which is likely to be more soluble in water: / , WM, ,7??? (a) con" CHC“ (b) CH30H C6H110H (061315 MgO (d) Can @ 3. (2 points) Indicate which of the following pairs of compounds is likely to be miscible: (a) H20 and CH3CH2CH2CH2CH2CH2CH2CH3 (b) Br; and HI (0) HF and CC14 /@i CC14 and Br; 4. (2 points) Two systems are set up with semipermeable membranes separating solutions of unequal concentrations ofNaCl. Each system has one solution that is 1.0 M and another solution that is 0.010 mM. They differ, however, in the temperatures at which they are maintained. One is held at 2°C and the other is held at 85°C. Which has the larger osmotic pressure? (a) The osmotic pressures are the same. b he hot system has the hlgher osmotic TCSSUIC. p (c) The cold system has the higher osmotic pressure. (d) No osmotic pressure exists in either system. NAME: 5. (2 points) Which of the following substances is a solid at 25°C and 1 atm? \\ 25 DC 6. (4 points) A test routinely done on new pharmaceuticals early in their development required the observation of their relative solubilities in octanol (Cngg) and water. A drug has to be sufficiently soluble in water (hydrophilic) to be canied in the blood stream but sufficiently hydrophobic (octanol-soluble) to move across cell membranes. Pick the molecule from the four drawn below that you predict might have comparable solubility in both solvents. l o N ' ll 0 HzNweH—cwo (C) (d) NAME: MES/1 I 7. (4 points) The normal temperature range of the liquid phase of pure water is 0°C to 100°C. Which of the following solutions will have the largest temperature range for the liquid state? ' Assume that the solutions all behave ideally. (a) 2 M aqueous fructose (the sugar in honey: C6H1205) solution (b) 1 M aqueous sodium fluoride solution ' '°"‘\ @}2 M aqueous formic acid (a weak acid) solution (d) 0.5 M aqueous sulfuric acid solution (6) 0.5 M aqueous potassium sulfate solution 8. (2 points) During a a' ASSM>0. b. ASsm<0, spontaneous chemical reaction, it is found that ASsyS < 0. This means 0. AS51le < 0 (and smaller than ASS“). 63. A851." > 0 (and larger than ASsyS)' 9. (2 points) The following figures show four boxes containing marbles. All of the marbles are identical. Which box has the lowest entropy? NAME: Egg] 10. (4 points) Indicate which of the following reactions result in a positive AS. AgCl(S) + NaNO3(aq) a. AgN03(aq) + NaCl(aq) HCl(aq) b. HCl(g) + H2001) A 2 H1(g) 0- H2(g) +12(g) @ cznzoxg) *—————* 2 CO(g) + H2(g) 11. (6 points) Dinitrogen tetroxide (N204) decomposes to nitrogen dioxide (N02). If AH = 58.02 kJ/mol and AS = 176.1 J/mol - K, at what temperature is this reaction at equilibrium? 4'3 5650C C. —272.70C b 329.5°C d. 250°C Calculation: AG :1 an ~T’AS2 O :3 £58.02. if;- > we TKQ-liiél M”) 55.02. awn/mag ””5; M 543mg adj—é»! era'fi " g I: 32.9.5”K, T‘s: 329.5”!!{a233‘gz 53.506: 12. (2 points) A reaction with a high enthalpy of reaction value is spontaneous at low temperature but becomes nonspontaneous at high temperature. What are the signs for AH" and AS" respectively? (a) (b) —,+ (d) +, + NAME: id— 13. (16 points) Given the following data, determine the rate law for the reaction NH4+(09) + NORM!) —> N2(g) + H20( 5) Experiment [NI-14+] (M) [NOZ] (M) Rate (Ms) 1 0.2500 0.2500 1.25 x 10'3 >0 *2 2 0.5000 0.2500 *2“ 2.5 x 10‘3 7‘2. 3 0.2500 0.1250 6. x 104‘ Wei ZNLLfJ i . + . ' mm x N0 “ @ktNm ][N02] 0 1:er rrNoz] E Z’ 1 c. k[NH4+][N02‘]m d. klNPhT/ZlNOz'] What is the overall order of the reaction? a. first order second order 0. third order d. order of 1.5 Calculate the value of k for the reaction: , g k: 0. 0200 N145” Calculations: max-M3 We: ~39; ([email protected])(O-2€DOW .. “5 is 2, ~i a, W: 5,325,930 8 (a .2. 5‘0 0 M 14. (2 points) The following graph shows the kinetics curves for the reaction of nitrogen with hydrogen to form ammonia: N2(g) + 3 H2(g) —% 2NH3(g). Which curve is nitrogen? Concentration ‘(c) c (d) none of these could be nitrogen (80 a NAME 1551’} 15. (14 points) Determine the first ionization energy of magnesium from the following data: Mg(S) + F203) —> MgF2(S) U = Lattice energy of Mng = — 2931.7 kJ/mol AHvap ofMg = 150.0 kJ/mol AHEZ ofMg+ = 1451 kJ/rnol AHBE osz = 154 kJ/mol AHEA ofF = -3 82 kJ/Inol AHrxn = — 1096.5 kJ/m01 Calculations: .n g ' A ”m AMW 4“ (Aqua? 41““:52) “5" Augg“ 2134-5574 ”5% ijggfi [(qu )1 (Mm-4 genome/L) + ;:{~ may @2931??? En maé ‘ ””6 Awas+flaz£$ m£ NAME: ii i 16. (17 points) You are a new intern working for Car Talk. Click and Clack take a call from a person from Hawaii who has just moved to Minnesota and is concerned about antifreeze in his radiator. The Magliozzi brothers are MIT grads in engineering and are totally capable of answering the question, but they are on the air and don’t have time to do the calculations. They know you are a Lehigh student and ask you to do your alrna mater proud by helping them out. The person has 2 gallons of ethylene glycol (HOCHZCHon: mol. wt: 62.07 g) and wants to mix up as much solution as possible. He also wants the solution to protect his radiator from freezing down to a temperature of —3 5°C. The person needs to have four questions answered: (a) How many liters of water does the person need to add to his supply of ethylene glycol to make a solution that will not freeze down to -35°C? (b) What is the total volume of solution in liters that he will be able to make? (c) Just out of curiosity, the caller also wants to know at what temperature (in 0C) the final solution of water and ethylene glycol will boil at atmospheric pressure. (d) The pressure in the radiator is actually much higher than atmospheric pressure. Will the boiling point of the fluid at the higher pressure be lower or higher than the value you calculate in (0)? Additional information you might find useful: 1 gallon = 4 quarts; approximate 1 quart = l L; 1 g H20 = 1 mL H20; density of ethylene glycol = 1.11 g/mL; Kf for water = —1.86°C/m; Kb for water = 0.520C/m. Calculations: (a) 3 ar Cs a $51910 a, s 1, C . ”a a? Emlmi 334% a maram b wag U Karma!“ 9'“ a? €ngL iooamé I-Ii Wag W xii, wijxéQ,Q¥a ”jggmg? l/OQC/ 56 #k’ H 0: me are l :4 .. - § 2 m Curég‘ 2a =~7~53€g=ififfll (d) (i) igher (ii) lower [qmrf la ) 1575,5410 4— 3r, g6? : Aié‘L gm [mm 4) C) 151T = (aerate { .: a , o o a QMQM) CMSC, To“ wooing? C .3 mffit =’-‘ M01: NAME K13? 17. (10 points) Deposits of elemental sulfur are often seen near active volcanoes. Their presence there may be due to the following reaction: SOz(g) + 2 H2805?) ——> 3 8(5) + 2 H20(g) (a) Calculate AH0 and ASO for this reaction. (b) Predict the temperature range over which this reaction is spontaneous. AHfo kJ/rnol 5° J/mol'K 8(5) 0.0 H20(g) -241.8 SOz(g) —298.8 H2$(g) -20.17 Work space: (a) 32.1 188.8 248.2 205.6 ARE“: flig‘frgkjm (b) sits/e 740 7% K, (4;???K 11130 3([3 (a .00) +52 meta] .... W... 273%} +9 (1.20.6131 >tj' 3‘ W“ [Lilia 5“ ET ASQ 3‘ [small +3 (188.85] «Er (wag; +3£ao§2a>j '49 .9, 9-: [2615 3731 == ”(MESS £37K“ m": Artemgaec «exfW All" : Tits" 7‘3 gag ”1%5‘1S‘U 45" «0456351231 =1 ?’%0 K. ‘ Ear-Am / 3. MIR: '. Isa/nib “W H306? 1665:6371, '5¥3C7Lo rm K. NAME: 16 18. (6 points) The following solutions are separated by a semipermeable membrane. In which direction will the solvent flow? (a) A = 4.68 M glucose; B = 3.00 M NaCl @ to B (ii) B to A (iii) no net flow (b) A = 100 mL of 0.392 M KNO3; B = 100 mL of 0.226 M NaZSO4 (i) A to B @ to A (iii) no net flow (c) A: 100 mL of1.10M LiClO4; B = 100 mL 1.10 MKF (i)Ato B (ii) BtoA '(iii) net flow 19. (2 points) At a certain time in the reaction 2 NO(g) + F2(g) '9 2 N02F(g) the rate of formation of product is 0.16 moi/L's. How fast is the F2 disappearing? (i). 0.16 mol/Ls (ii) 0.32 mol/Ls 6119* .080 inol/Ls (iv) 0.48 mol/Ls 10 ...
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