Go on to the next page. Chemistry 112 Name Exam I Form A Section February 1,

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1 Chemistry 112 Name Exam I Form A Section February 1, 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. CHEMISTRY 112 EXAM 1 Feb. 1, 2012 FORM A 1. Consider the following reaction: 2 NOBr (g) 2 NO(g) + Br 2(g) When the rate of appearance of Br 2(g) is 0.10 M s 1, what is the rate of disappearance of NOBr(g)? A M s 1 B M s 1 C M s 1 D M s 1 E M s 1 2. Consider the reaction: A B The rate of the reaction is 2.4 x 10 2 M/s when the concentration of A is 0.15 M. What is the rate constant if the reaction is second order in A? There are 24 questions on this exam. Check that you have done all of the problems and filled in the first 24 bubbles on the scantron.your score will be reported in percent (max 100%). Exam policy Hints 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 the web after the exam (on the Exam Schedule page). You must turn in your cover sheet with your scantron answer form. 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. A. 2.9 M 1 s 1 B. 1.1 M 1 s 1 C M 1 s 1 D M 1 s 1 E M 1 s 1

2 3 The loss of reactant A is measured over time to determine the rate constant for the second-order reaction A B. Which of the following best resembles the expected results? A. B. 5. An intermediate: A. lowers the overall enthalpy of a chemical reaction. B. increases the energy of the final products. C. is produced in one reaction, and consumed in a later reaction. D. is represented by the highest energy point in a reaction coordinate diagram. E. none of the above 6. In general, as the reaction progresses and more reactant is converted to product C. D. E. none of the above represents the expected results. 4. Below are five statements about the temperature dependence of a reaction rate constant, k. Which statement holds true for most chemical reactions? A. k increases with temperature, mainly because there are fewer collisions per second B. k increases with temperature, mainly because a higher proportion of the collisions are energetic enough to produce reaction. C. k decreases with temperature, mainly because of the decrease in the effectiveness of the attractive long-range intermolecular forces D. k does not change with temperature E. k increases or decreases with temperature, depending on whether the reaction is endothermic or exothermic A. The rate of loss of reactants decreases. B. The rate of appearance of product decreases. C. The rate of appearance of product increases. D. Both A and B E. Both A and C 7. Chlorine dioxide (ClO 2) is a disinfectant used in municipal water-treatment plants. It dissolves in basic solution, producing ClO 3 and ClO 2 according to the reaction: 2 ClO 2(aq) + 2OH (aq) ClO 3 (aq) + ClO 2 (aq) + H 2O(l) The following kinetic data were obtained at 298 K for the reaction: Experiment [ClO 2] (M) [OH ] (M) Initial rate (M/s) What is the rate constant for this reaction? A. 3.5 x 10 2 s 1 B. 42 s 1 C. 14 M 1 s 1 D. 9.2 M 1 s 1 E. 1.7 M 2 s 1

3 8. Consider the following reaction and rate law: A + B C rate = k [A] 2 [B] The units of the rate constant k will be: A. M s 1 B. s 1 C. M 1 s 1 D. M 2 s 1 E. rate constants are unitless 9. The initial step in the formation of smog is the reaction between nitrogen and oxygen: N 2(g) + O 2(g) 2 NO(g) The temperature dependence on the rate constant was determined, yielding the graph: 10. Which of the following statement(s) are true about the reaction coordinate diagram below? i. the reaction is exothermic ii. there are three transition-states iii. the second step is the slow step A. i only B. ii only C. iii only D. i and ii E. ii and iii 11. In the following mechanism for NO formation, oxygen atoms are produced by breaking O=O bonds at high temperature. Consider the following: Overall: N 2(g) + O 2(g) 2 NO(g) First Step: O 2(g) 2O(g) (fast equilibrium) Second Step: O(g) + N 2(g) NO(g) + N(g) Third Step: N(g) + O(g) NO(g) The experimentally determined rate law is: rate = k[n 2][O 2] 1/2. If the above mechanism is correct, which step must be rate-determining? The slope of the plot is 3.78 x 10 4, and the y-intercept is Which of the following statements is true about the activation energy, E a, and the frequency factor, A? A. E a = 37.8 kj/mol, A = 24.6 B. E a = 37.8 kj/mol, A = 24.6 C. E a = 24.6 kj/mol, A = 3.78 x 10 4 D. E a = 242 kj/mol, A = 2.99 x 10 8 E. E a = 314 kj/mol, A = 4.83 x A. first-step is rate-determining B. second-step is rate-determining C. third-step is rate-determining D. the proposed mechanism is not consistent with the overall reaction E. the proposed mechanism is not consistent with the experimentally determined rate law

4 12. Chlorofluorocarbons (CFCs) contribute to the destruction of the ozone layer by releasing chlorine atoms. Consider the following: 2 O 3 (g) 3 O 2 (g) (overall process) Free chlorine atoms react with ozone, forming chlorine monoxide: Cl(g) + O 3(g) ClO(g) + O 2(g) Chlorine monoxide then reacts with ozone producing oxygen and regenerating atomic chlorine: ClO(g) + O 3(g) Cl(g) + 2 O 2(g) Which of the following statements is true about the above processes? A. Cl(g) is a homogenous catalyst B. ClO(g) is a heterogenous catalyst C. Cl(g) is an intermediate D. O 3(g) is an intermediate E. there are neither catalysts nor intermediates for this reaction 13. The thermal decomposition of phosphine (PH 3) into phosphorous and hydrogen gas is a first-order reaction: 4 PH 3(g) P 4(g) + 6 H 2 (g) The rate constant is 1.98 x 10 2 s 1. What is the time required for 95 percent of the phosphine to react? A. 151 s B. 110 s C. 49 s D. 27 s E s 14. For the reaction 2 H 2(g) + 2 NO(g) N 2(g) + 2 H 2O(g) the experimentally determined rate law is rate = k [H 2][NO] 2. Three mechanisms have been proposed: Mechanism I H 2 + NO H 2O + N (slow) N + NO N 2 + O (fast) O + H 2 H 2O (fast) Mechanism II 2 NO N 2O + O (slow) H 2 + O H 2O (fast) N 2O + H 2 N 2 + H 2O (fast) Mechanism III 2 NO N 2O 2 (fast equilibrium) N 2O 2 + H 2 N 2O + H 2O (slow) N 2O + H 2 N 2 + H 2O (fast) Which of the proposed mechanisms is consistent with the experimentally determined rate law? A. I only B. II only C. III only D. I and II E. II and III 15. The enzyme carbonic anhydrase catalyzes the reaction: CO 2(g) + H 2O (l) HCO 3 (aq) + H + (aq) Without the enzyme, the reaction proceeds with a rate constant of s 1 at 25 o C. In the presence of enzyme, the reaction proceeds with a rate constant of 1.0 x 10 6 s 1 at 25 o C. Assuming the collision factor is the same for both situations, what is the difference in the activation energies for the uncatalyzed versus enzyme-catalyzed reaction (i.e. E a = E a (without enzyme) E a (with enzyme) ) at 25 o C? A. 14 kj/mol B. 42 kj/mol C. 55 kj/mol D. 120 kj/mol E. 420 kj/mol

5 16. Radium undergoes alpha decay. The product of this reaction also undergoes alpha decay. What is the product of the second decay reaction? A. Po B. Rn C. Ra D. U E. Th 17. Which of the following statements concerning the nuclear reactor is (are) false? 1. Pure 235U is used as the fuel in the reactor. 2. The control rods present in the reactor absorb excess neutrons. 3. Even during "melt-down", the reactor cannot explode like a nuclear bomb. 4. Water cannot be used as a coolant for the reactor core. A. 1 only B. 3 only C. 1 and 3 D. 1 and 4 E. 3 and When copper-59 undergoes positron emission, the immediate nuclear product is A. Nickel-59 B. Nickel-58 C. Copper-58 D. Zinc-59 E. Zinc The most probable mode of decay of 131I is A. alpha emission B. beta emission C. positron emission D. neutron emission E. electron capture 20. You can increase the rate of radioactive decay of 90 Sr in a sample of nuclear waste by: A. increasing the temperature B. applying pressure C. placing the radioactive nuclei in a magnetic field D. placing the radioactive nuclei in an electric field E. none of the above will increase the rate of radioactive decay 21. The bombardment of uranium-235 with a neutron generates tellurium-135, 2 neutrons, and A. Strontium-103 B. Krypton-101 C. Krypton-103 D. Strontium-99 E. Zirconium Pb has a half-life of 22.3 years and decays to form 206 Hg. If you start with 7.50 g of 210 Pb, how many grams of 206 Hg will you have after 17.5 years? A B C D E Go on to the last page

6 23. Enzymes: A. slow down chemical reactions B. change the equilibrium position of a reaction to favor the products C. can lower the activation energy of the reaction D. increase the activation energy of the reaction E. are produced in one reaction and consumed in a later reaction 24. What is the binding energy per nucleon of a chlorine-35 atom with an atomic mass of amu? A x J/nucleon B x J/nucleon C x J/nucleon D x J/nucleon E x J/nucleon END OF EXAM