Chemistry 112 Name Practice Exam 1C Section

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1 Chemistry 112 Name Practice Exam 1C Section IMPORTANT: On the scantron (answer sheet), you MUST clearly fill your name, your student number, section number, and test form (white cover = test form A; yellow cover = test form B). Use a #2 pencil. There are 25 questions on this exam. Check that you have done all of the problems and filled in the first 25 bubbles on the scantron BEFORE TIME IS CALLED. The maximum score on this exam is 25 points. Your score will be reported in percent (max 100%). Exam policy Calculators with text-programmable memory are not allowed. Relevant data and formulas, including the periodic table, are attached at the end of this exam. Your grade will be based only on what is on the scantron form. The answer key will be posted on ANGEL after the exam. You have 75 minutes to complete this exam. You must completely fill in your scantron bubbles before the 75 minute period has ended. You must turn in your cover sheet with your scantron answer form. Hints As you read the question, underline or circle key words to highlight them for yourself. Avoid errors from "mis-reading" the question. Pay attention to units and magnitudes (decimal places) of numbers obtained from calculations. There is no penalty for guessing. Circle the answer you choose so that you can grade yourself using the answer key posted after the exam.

2 CHEMISTRY 112 Practice Exam 1C Spring What is X in the nuclear reaction below? 56 Fe + 2 H X + 4 2α A. 58 Ce B. 54 Mn C. 54 Co D. 58 Mn E. 52 Fe 2. The isotope cobalt-60 is most likely to decay via which of the following decay modes? A. α-decay B. β-decay C. Positron emission D. Electron capture E. Nuclear fusion 3. In the figure below, which letter corresponds to a transition state (or activated complex)?

3 Which one of the following statements regarding nuclear decay is TRUE? A. The half-lives of radioactive nuclei can be shortened significantly through increased temperature, concentration, and catalysis. B. Nuclear fusion is when a large nucleus is split into two or more small nuclei and one or more neutrons. C. Nuclear decay kinetics are second order. D. β-decay results in a net increase of nuclear charge. E. Positron emission and α-decay both result in a net increase in the numbers of neutrons in a nucleus. 5. An exothermic one-step reaction has an activation energy of 30 kj/mol and a ΔH of 15 kj/mol in the forward direction. A catalyst lowers the activation energy of both the forward and reverse directions by 10 kj/mol. What is the activation energy of the reverse catalyzed reaction? A. 30 kj/mol B. 55 kj/mol C. 45 kj/mol D. 35 kj/mol E. 15 kj/mol 6. Which of the following statements are true regarding enzymes? i. Enzymes make a reaction more favorable by lowering the energy of the products. ii. Enzymes increase the K eq of a reaction. iii. Enzymes lower the activation energy, E a, of a reaction. iv. Enzymes can increase the Arrhenius Factor (frequency factor), A, of a reaction. A. ii only B. iii only C. i and iv only D. iii and iv only E. i, ii, and iii only

4 7. Consider the following reaction, whose rate law is given by rate = k[no] 2 [Cl 2 ]. What are the units of the rate constant, k? 2 NO (g) + Cl 2 (g) 2 NOCl (g) A. s 1 B. M 1 s 1 C. M 2 s 1 D. M 3 s 1 E. M 2 s 1 8. Two substances A and B react with each other. In 33 minutes, A is 50% consumed. After a total of 66 minutes, A is 75% consumed. Changing the concentration of B has no effect on the results. Which statement is true about the rate law of this reaction? A. This reaction is zeroth order in both A and B. B. This reaction is 1st order in both A and B. C. This reaction is 2nd order in both A and B. D. This reaction is 1st order in A and zeroth order in B. E. This reaction is 2nd order in A and zeroth order in B Hydrogen reacts with nitrogen monoxide via the following equation: 2 H 2 (g) + 2 NO (g) N 2 (g) + 2 H 2 O (g) The following mechanism is proposed to describe this interaction: Which rate law is consistent with this mechanism? A. rate = k[h 2 ][NO] 2 B. rate = k[h 2 ][N 2 O 2 ] C. rate = k[h 2 ][NO] D. rate = k[h 2 ][N 2 O] 2 NO N 2 O 2 (fast equilibrium) N 2 O 2 + H 2 N 2 O + H 2 O (slow) N 2 O + H 2 N 2 + H 2 O (fast) E. rate = k[no] 2

5 10. The data below were collected for the following reaction: A (aq) 2 B (aq) y-intercept = 0.58, slope of trend line = s 1 y-intercept = , slope of trend line = M 1 s 1 The slopes of the trend lines are given. Given these data, if a grad student studying this reaction has an initial concentration of [A] o = 3.2 M, what will be the concentration of A after 500 seconds? A. 5.0 x 10 2 M B M C M D. 2.9 x 10 2 M E. 2.6 x M 11. Acetaminophen (Tylenol ) is eliminated from the cerebrospinal fluid of the body with a first-order half-life of 3.2 hours. If the concentration of acetaminophen inside a patient is 20 µl/ml at 1:00 pm, what will be the concentration at 11:00 pm? A µl/ml B µl/ml C µl/ml D µl/ml E. It will be completely eliminated by 11:00 pm, and the concentration will be 0 µl/ml.

6 12. Dr. Julius Antihaber is a scientist interested in converting ammonia (NH 3 ) to its elemental components. He creates a reaction chamber that is specifically designed to monitor the concentration of components in a reaction. The following pictures represent his results at two points in time, where each drawing of a molecule represents 1 M of molecules. (i.e. the initial concentration of ammonia is 4 M.) t = 0 sec t = 45 sec = 1 M ammonia (NH 3 ) What is the average rate of disappearance of ammonia over the 45 seconds of reaction? A x 10 2 M/s B x 10 2 M/s C x 10 2 M/s D x 10 2 M/s E x 10 2 M/s 13. Iridium-192 is one of the more stable isotopes of iridium and is utilized in brachytherapy, a form of cancer radiotherapy where a sealed radiation source is placed inside or next to the area requiring treatment in the body. Iridium-192 has a half life of 73.8 days. What percentage of iridium-192 remains in the body after 1 year has passed? A. 7.2% B. 50.0% C. 99.1% D. 3.3% E. All of the iridium-192 has decomposed.

7 14. An important reaction was run at different temperatures and an Arrhenius plot was made: slope of trend line: 3412 K y-intercept of trend line: 2 What is the activation energy of this important reaction? A kj/mol B kj/mol C kj/mol D kj/mol E. 241 kj/mol 15. Rick T. Cat decided to visit the dwarf planet of Pluto and brought back a space rock! Upon analysis, the rock is found to contain 5.51 mg of uranium-238 and 1.63 mg of lead-206. Assuming that the mineral sample started as pure uranium-238, what is the age of the Plutonian rock? The half-life for the process uranium-238 lead-206 is 4.5 x 10 9 years. A. 1.9 x 10 9 years B. 4.5 x 10 9 years C. 1.7 x 10 9 years D. 2.3 x 10 7 years E. 8.8 x 10 6 years

8 16. S N 1 substitutions represent an important class of reactions in organic chemistry. Consider the following S N 1 reaction, which is first order with respect to 2-bromobutane, C 4 H 9 Br. The concentration of water in the reaction has no effect on the reaction rate. A scientist runs this reaction at a high temperature and finds that when [C 4 H 9 Br] = 0.31 M, the reaction rate is M/sec. What is the value of the rate constant, k, at this temperature? A. 19 s 1 B. 5.0 x 10 3 s 1 C. 9.3 s 1 D. 5.2 x 10 2 s 1 E. 1.7 x 10 1 s What is the nuclear binding energy in J/nucleon of iodine-127? The atomic mass of one iodine-127 nucleus is amu. A x 10 6 J/nucleon B x 10 6 J/nucleon C x J/nucleon D x J/nucleon E x J/nucleon

9 18. Consider the generic reaction: 2 A + B + 2 C Products This reaction was performed under 4 different sets of conditions, and the following data were obtained: Experiment # [A] (M) [B] (M) [C] (M) Rate (M/s) x x x x 10 3 Using these data, what is the overall rate law for this reaction? A. Rate = k[a][c] 2 B. Rate = k[a][b] 2 [C] 2 C. Rate = k[a] 2 [B][C] 2 D. Rate = k[a] 2 [C] E. Rate = k[a] 2 [B] 1/2 [C] 19. Pseudomonas spp. is a genus of bacteria known to cause spoilage in Mediterranean fish. The activation energy for the reaction that leads to spoilage has been measured to be 80 kj/mol. How many times faster would the spoilage of Red Mullet (a species of Mediterranean fish) occur at the balmy 26 o C of Forum Building than at 4 o C (a standard refrigerator temperature)? A B. 7.2 C D. 112 E x 10 3

10 A team of intrepid graduate students in the lab of Rick T. Cat are working to elucidate a much sought-after mechanism for a very important reaction regarding the decomposition of ozone (O 3 ) in the presence of NO (g). They collect the following data using reaction progress kinetic analysis: Each peak represents a step in the mechanism. Is this reaction endothermic or exothermic, and what is the rate-limiting step in the forward direction? enthalpy rate-limiting step A. exothermic first B. endothermic first C. endothermic second D. exothermic second E. endothermic third 21. The proposed steps of the ozone decomposition that Dr. Cat s grad students discovered are: Step 1: O 3 (g) + NO (g) O 2 (g) + NO 2 (g) Step 2: NO 2 (g) NO (g) + O (g) Step 3: O (g) + O 3 (g) 2 O 2 (g) Based on this proposed mechanism, what (if any) is the catalyst and what are the intermediates? Catalyst Intermediate(s) A. O 3 (g) NO 2 (g), O (g) B. NO (g) NO 2 (g), O (g) C. NO 2 (g) O (g), NO (g) D. NO (g) NO 2 (g), O 2 (g) E. none NO 2 (g), O (g), NO (g) ---

11 A reaction utilizing sulfuric acid as a reactant is studied at 25 o C, and the following data were obtained and graphed: slope of trend line: M 1 s 1, y-intercept of trend line: A scientist then runs the same reaction at the same temperature but with a different initial concentration of H 2 SO 4. If the initial concentration of [H 2 SO 4 ] o = 18 M, how long will it take for 75% of this reagent to be used up? A. 3.3 sec B. 42 sec C. 12 sec D. 1.5 sec E. 5 sec 23. Meet Dr. Rick T. Cat, a Distinguished Professor of Science with a taste for adventure and a knack for sustainability! His lab has been working on a way to improve the decomposition of polyethylene terephthalate (PET), a polymer used in soft drink bottles. The activation energy for uncatalyzed degradation of PET via glycolysis is 46.2 kj/mol. However, the Cat Lab has developed a [Rick T.] catalyst to lower the activation energy to 26.2 kj/mol! Assuming that the Arrhenius factor A is unchanged by the catalysis, how many times faster will the catalyzed decomposition of PET proceed at 25 o C? A. The catalyzed and un-catalyzed reactions will proceed at the SAME rate. B. 1.8 times faster C. 20 times faster D. 10,000 times faster E. 3,200 times faster

12 24. The following graph describes the variation in the concentration of reactant A over time for the reaction below. What are the rate law and the value of k for this reaction? 2 A (aq) 2 B (aq) Rate Law Value of k A. Rate = k[a] 1.0 s 1 B. Rate = k[a] s 1 C. Rate = k[a] M 1 s 1 D. Rate = k[a] M 1 s 1 E. Rate = k[a] 2 [B] M 3 s A ml flask is filled with moles of A and allowed to react to form B according to the reaction below. The following experimental data are obtained for the number of moles of A as the reaction proceeds. What is the average rate of appearance of B in units of M/s between t = 10 min. and t = 30 min.? Assume that the volume of the flask is constant. A(g) 3 B(g) Time (minutes) Moles of A A. 3.0 x 10 5 M/s B. 2.3 x 10 2 M/s C. 1.3 x 10 5 M/s D. 3.8 x 10 4 M/s E. 4.2 x 10 4 M/s --- END OF EXAM ---

13 Exam 1 Practice Exam C KEY 1. B 2. B 3. B 4. D 5. D 6. D 7. C 8. D 9. A 10. B 11. C 12. E 13. D 14. B 15. A 16. D 17. E 18. D 19. C 20. A 21. B 22. E 23. E 24. A 25. D