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Unformatted text preview: Name_______Key__________________ Student ID Number___________________________ Lab TA Name and Time_______________________ Professor Susan Kauzlarich Spring 2009 CHEMISTRY 2C (Section B) Exam II Instructions: CLOSED BOOK EXAM! No books, notes, or additional scrap paper are permitted. All information required is contained on the exam. Place all work in the space provided. If you require additional space, use the back of the exam. (1) Read each question carefully. (2) There is no partial credit for the problems in Part I and Part II. (3) The last page contains a periodic table and some useful information. You may remove this for easy access. (4) If you finish early, RECHECK YOUR ANSWERS! U.C. Davis is an Honor Institution Possible Points 1–11. 33 points 12–13. 20 points 14–16. 22 points 16–17. 16 points 18. 15 points Total Score (106) Points Multiple Choice (circle one) 1. 2. 3. 4. 5. 6. 7. 8. 9. a a a a a a a a a b b b b b b b b b b b cd cd cd cd cd cd cd cd cd cd cd e e e e e e e e e e e 10. a 11. a Exam II Page 2 of 9 Part I: Multiple Choice, Concepts 1. Circle the correct answer and enter your response on the cover – No partial credit Define activation energy. A. the difference between the energy of the products and reactants B. the energy difference between the maximum energy of reaction and the energy of the products C. the minimum total kinetic energy that molecules must bring to their collisions for a chemical reaction to occur D. the total kinetic energy of molecules in collisions E. the total kinetic energy of molecules in a system Which of the following metals reacts most violently with water? A. Cs B. Na C. Mg D. Ba E. None of the Above In the first order reaction, A ––> products, [A] = 0.400 M initially and 0.250 M after 15.0 min, what will [A] be after 175 min? A. 1.67 x 10–3 M B. 1.04 x 10–3 M C. 3.70 x 10–2 M D. 6.024 x 10–3 M E. 2.31 x 10–1 M The reaction 2H2 + NO ––> H2O + 0.5N2 is first order in H2 and second order in NO. The rate law is: A. k[H2]2[NO] B. k[H2][NO]2 C. k[H2] D. k[H2][NO] E. k[H2O][N2]0.5 White and red phosphorus are examples of? A. isotopes B. allotropes C. enantiomers When A. 90 38 2. 3. 4. 5. D. isomers E. polymorphs 6. 89 39 Sr undergoes positron emission, the product nucleus is: 90 B. 37 Rb C. 391Sr D. 90Y E. Y 8 39 89 38 Sr ! ! ! ! ! ! Exam II 7. [Co(CN)6]4– has how many unpaired electrons? A. 2 B. 1 C. 4 D. 3 8. Page 3 of 9 E. none of the above Use VSEPR theory to predict the probable geometric structure of the molecule O2XeF2? A. Trigonal planar B. T-shape C. Trigonal bipyramidal D. See-saw E. None of the above What is the rate law for the following reaction, given its mechanism: N2O + NO ––> N2 + NO2 (overall) N2O + NO ––> N2ONO* (slow, elementary step) N2ONO* ––> N2 + NO2 (fast, elementary step ) A. Rate = k[N2O] B. Rate = k[N2O]2 C. Rate = k[NO]2 D. Rate = k [N2O][NO] E. Rate = k[N2ONO*] For the reaction: 2N2O5 ––> 4NO2 + O2 the rate law is rate = k[N2O5]. At 300 K, the halflife is 2.50 x 104 s and the activation energy is 103.3 kJ/mol. What is the rate constant at 350 K? A. 4.78 s–1 B. 2.79 x 10-5 s–1 C. 6.38 x 10–6 s–1 D. 7.47 x 10–8 s–1 E. 1.03 x 10–2 s–1 P4O6 reacts with water to produce: A. HPO3 B. H3PO4 C. H3PO3 D. H4P2O7 E. None of the above. 9. 10. 11. Exam II Page 4 of 9 Part II: Short Answer Fill in the blank 12. (12 points) Reactions: fill in the blank with the appropriate molecule(s) and balance the reactions. CO2 + H2O H2CO3 Ca + H2 CaH2 Na2O + H2O 2 NaOH 2Al + 3 Cl2 Al2Cl6 13. (8 points) Nuclear reactions: fill in the blank with the appropriate nuclei or particle. 23 11 Na + 2 1 H ––> 24 11 Na + 1 1 H ! 238 92 ! U ! ! U+ 59 27 Co + + 1 56 !n ––> 2!Mn 0 5 + 4 2 He ! ! 238 92 H ––> ! 2 1 240 94 Pu + ! 0 –1 " 14 7 N! 246 1 ––> !99 Es + 6 0 n ! ! ! ! Exam II Page 5 of 9 14. (10 points) Draw the reaction profile that fits all the constraints given below. Label the axes, reactants, products, intermediate, and ΔH. Thermodynamically favorable One intermediate Two transition states Ea uncatalyzed Potential Energy Reactants ∆H Intermediate Ea catalyzed Products Progress of reaction 15. (6 points) Using dotted lines, show what happens if the reaction described above had a catalyst added. Assume that the catalyst only speeds up the second step in the overall reaction. Indicate any important parameters. Ea (activation energy) is lowered 16. (6 points) Given that 2NO(g) + Cl2(g) 2NOCl(g). Determine orders of reaction with respect to each reactant. Also, find k. Write your answers in the box provided. Include units. Experiment [NO], M [Cl2], M Initial rate, M / s Answers: 1 0.0125 0.0255 2.27 x 10–5 2 0.0125 0.0510 4.55 x 10–5 k = 5.70 s–1M–2 3 0.0250 0.0255 9.08 x 10–5 order for [NO] = 2 order for [Cl2] = 1 Exam II Page 6 of 9 Part III: Long Answer Please show all work – Partial credit 16. (11 points) Given: [Ni(CN)4]2–. Write your answers in the boxes. A. (2 points) What is the electronic configuration of Ni? [Ar]3d8 B. (2 points) List the most likely molecular (geometric) shape: Square planar C. (2 points) Paramagnetic or diamagnetic? diamagnetic D. (5 points) Draw and label all parts of the Crystal Field Splitting diagram. Put in the correct number of electrons. dx2–y2 17. [5 points possible] The following data were collected for the reaction H2(g) + I2(g) 2HI(g) at 780 K: Time, s 0 1 2 3 4 [I2], mmol/L 1.00 0.43 0.27 0.20 0.16 dxy dz2 dxz, dyz (a) Plot the data to CONFIRM that the reaction is second order. Completely label the graph, including k and [Ao]. 6 1 [ I2 ] 4 2 0 0 1 2 t(s) 3 4 5 6 Slope = k Intercept = 1 [ I 2 ]0 ! Exam II Page 7 of 9 18. (15 points) The gas-phase reaction of chlorine with chloroform is described by the reaction. Cl2(g) + CHCl3(g) ––> HCl(g) + CCl4(g) A proposed mechanism for this reaction follows: Cl2(g) 2Cl(g) fast equilibrium Cl(g) + CHCl3(g) ––> HCl(g) + CCl3(g) slow CCl3(g) + Cl(g) ––> CCl4(g) fast A. (3 points) Is this an acceptable mechanism? Explain or show why. Yes, the three steps add up to the overall reaction B. (4 points) Write the rate equation of each reaction below, Call equilibrium step: 1(forward), -1(reverse), then steps 2 and 3: Rate1 = k1[Cl2] Rate –1 = k–1[Cl]2 Rate2 = k2[Cl][CHCl3] Rate3 k3[CCl3][Cl] C. (2 points) Identify the intermediate(s), if any. Cl(g), CCl3(g) D. (6 points) Derive the rate law. Slow step: rate = k2[Cl]CHCl3] Equilibrium: k1[Cl2] = k–1[Cl]2, solve for [Cl]: 1 " k1 % rate = k2 $ ' [Cl2 ] 2 [CHCl3 ] # k–1 & 1 2 " k1 % [Cl ] = $ [Cl2 ]' # k–1 & 1 2 ! ! Exam II Page 8 of 9 Spectrochemical Series: CN->CO>NO2->en>NH3>H2O>ox2->OH->F->SCN->Cl->Br->IConstants: R = 8.3145 J / mol K R = 0.08206 L atm / mol K h = 6.626 x 10-34 J s Equations: Δ = h c / λ (first order) ln [A]t = ln [A]o – kt t1/2 = (ln 2) / k (zero order) [A]t = [A]o – kt t1/2 = [A]o/2k (second order) [A]t-1 = [A]o-1 + kt t1/2 = 1 / (k[A]o) F = 96,485 C / mol ec = 2.9979 x 108 m / s Ea k = Ae RT ! (radioactive decay) ln Nt = ln No – λt t1/2 = 0.693 /λ & k' # E & 1 1 # ln$ ! = a $ ' ! % k " R % T T' " 800 620 o y 580 r 400 v b g 490 430 560 Exam II Page 9 of 9 ...
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This note was uploaded on 10/23/2009 for the course CHE CHE 2B taught by Professor Toupadakis during the Winter '09 term at UC Davis.

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