Chemistry 112 Name Exam I Form A Section January 29, 2013 email 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.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.
CHEMISTRY 112 EXAM 1 January 29, 2013 FORM A 1. Consider the following reaction: A + B C Rate = k[b] 2 Which of the following will NOT increase the reaction rate? A. Increasing the concentration of A B. Increasing the concentration of B C. Raising the reaction temperature D. Adding a suitable catalyst E. All of the above changes will result in an increase in reaction rate 2. A possible mechanism for the reaction of hydrogen bromide with oxygen is: HBr (g) + O 2 (g) HOOBr (g) step 1 HOOBr (g) + HBr (g) 2 HOBr (g) step 2 HOBr (g) + HBr (g) H 2 O (g) + Br 2 (g) step 3 Which of the following is an intermediate in this reaction? A. HOOBr only B. HBr and O 2 only C. HOBr only D. HOOBr and HBr only E. Br 2, HOBr and HOOBr only 3. Which one of the following statements about rate constant k is FALSE? A. k is dependent on the concentration of the reactants. B. k increases with increasing temperature. C. k decreases with increasing activation energy. D. k can be increased by adding a catalyst. E. The reaction rate is directly proportional to k.
4. For the reaction below, = 2.5 x 10 2 atm/s, where ΔP(H 2 ) is the change in pressure of hydrogen. What is the rate of loss of C 6 H 14 (defined as ) for this reaction for the same time period? C 6 H 14 (g) C 6 H 6 (g) + 4 H 2 (g) A. 2.5 x 10 2 atm/s B. 6.25 x 10 3 atm/s C. 2.5 x 10 2 atm/s D. 0.10 atm/s E. 2.6 x 10 3 atm/s 5. For the following nuclear reaction, what is the value of x? A. 1 B. 3 C. 5 D. 7 E. 9 15 6. Given the initial rate data shown in the table below, what is the rate law of the following reaction? A. Rate = k[a][b] 2 Experiment [A] (M) [B] (M) Initial Rate (M/s) 1 0.1 0.2 1.2 x 10 4 2 0.1 0.4 4.8 x 10 4 3 0.2 0.2 1.2 x 10 4 B. Rate = k[a] 2 [B] C. Rate = k[a] 2 D. Rate = k[b] 2 E. Rate = k[b]
7. Which points on the reaction profile below represent intermediates? A. C and E only B. B, D and F only C. A and G only D. B, C, D, E and F only E. D only 8. Consider the reaction below: Br 2 (aq) + HCOOH (aq) 2 Br (aq) + 2 H + (aq) + CO 2 (g) Why does the instantaneous reaction rate for this chemical reaction decrease with time? (Assume temperature is constant.) A. The activation energy increases. B. CO 2 gas is escaping into the atmosphere. C. The concentration of Br 2 decreases. D. The HCOOH is a catalyst. E. ΔE for the reaction increases.
9. What type of particle or radiation is emitted when a F-20 nucleus decays to Ne-20? A. alpha B. beta C. neutron D. positron E. proton 10. The first-order reaction A B in which A molecules (black circles) are converted to B molecules (white circles) in a 2.0 L container is shown below at two points in time. What is the concentration of A molecules after 40 seconds? A. 8.0 molecules/l B. 4.0 molecules/l C. 2.0 molecules/l D. 12 molecules/l E. 6.0 molecules/l t = 0 s t = 20 s Go on to the next page
11. A reaction has the following rate law: Rate = k[a][b] 2 In experiment 1, the concentrations of A and B are both 0.10 M. In experiment 2, the concentrations of A and B are both 0.30 M. If the temperature stays constant, what is the value of the ratio? A. 3.0 B. 6.0 C. 9.0 D. 18 E. 27 12. What does a catalyst do? A. It lowers the overall enthalpy of the reaction. B. It lowers the activation energy of the forward reaction only. C. It raises the activation energy of the reverse reaction only. D. It lowers the activation energy of both the forward and reverse reactions. E. It raises the energy of the reactant molecules. -------------------------------------------------------------------------------------------------------------- 13. Why does the rate of a reaction increase with increasing temperature? A. The reactant molecules collide less frequently. B. The reactant molecules collide with greater energy. C. The activation energy is lowered. D. The reactant molecules collide with the right orientation. E. The concentration of the reactant molecules increases. Go on to the next page
14. What is the nuclear binding energy per nucleon, in joules, for a 25 Mg nucleus? (nuclear mass 24.985839 amu) [Use the following data: proton (mass) = 1.007825 amu; neutron (mass) = 1.008665 amu] A. 0.22076 J/nucleon B. 3.25 x 10 11 J/nucleon C. 1.32 x 10 12 J/nucleon D. 0.999 J/nucleon E. 2.64 x 10 12 J/nucleon 15. Iodine-131, t 1/2 = 8.0 days, is used in the diagnosis and treatment of thyroid gland diseases. If a laboratory sample of iodine-131 initially emits 9.95 x 10 18 β particles per day, how long will it take for the activity to drop to 6.22 x 10 17 β particles per day? A. 2.0 days B. 16 days C. 32 days D. 128 days E. 64 days Go on to the next page
16. The decomposition of NO 2 was studied at 656 K and the data was plotted below: (M 1 ) The y-intercept of the plot is 9.20 M 1, and the slope of the line is 10.16 M 1 sec 1. For a different experiment at the same temperature and an initial NO 2 concentration of 0.200 M, how long would it take to decompose half of the NO 2? A. 15.1 sec B. 5.62 sec C. 1.39 sec D. 0.492 sec E. 0.068 sec 17. The only stable isotope of aluminum is 27 Al. What type of radioactive decay would 23 Al be expected to undergo? A. proton emission B. neutron emission C. beta decay D. positron emission E. alpha decay Go on to the next page
18. The temperature dependence of the rate constant for a second order reaction is plotted below: The y-intercept of the plot is 23.2, and the slope of the line is 1.61 x 10 4 K. Based on this data, what would the rate constant be at 500 K? A. 1.23 x 10 4 M -1 s 1 B. 2.95 x 10 2 M -1 s 1 C. 3.49 x 10 1 M -1 s 1 D. 4.77 M 1 s 1 E. 5.11 x 10 3 M 1 s 1 19. Potassium-40 undergoes positron emission to form argon-40 with a half-life of 1.2 x 10 9 years. If a sample of rock from an asteroid contains 82% argon with the remaining portion being potassium, what is the age of the rock? (Assume that all of the argon in the sample is the result of potassium decay.) A. 3.4 x 10 8 years B. 2.1 x 10 9 years C. 8.3 x 10 8 years D. 1.5 x 10 6 years E. 3.0 x 10 9 years Go on to the next page
20. What is the balanced nuclear equation represented by the following diagram? A. B. C. D. E. Go on to the next page
21. For the overall reaction 2 N 2 O 5 (g) 4 NO 2 (g) + O 2 (g) the following mechanism is proposed: N 2 O 5 (g) NO 2 (g) + NO 3 (g) (fast equilibrium) NO 2 (g) + NO 3 (g) NO 2 (g) + NO (g) + O 2 (g) (slow) NO 3 (g) + NO (g) 2 NO 2 (g) (fast) Which statement is true about the rate law that is consistent with this mechanism? A. The rate law is first order in N 2 O 5. B. The rate law is second order in NO 2 and first order in NO 3. C. The rate law is first order in NO 2 and NO 3 and second order in N 2 O 5. D. The rate law is second order in N 2 O 5. E. None of these choices is consistent with the rate law. 22. The isomerization of methyl isocyanide, CH 3 NC CH 3 CN, follows first-order kinetics. The halflives were found to be 161 min at 199 C and 12.5 min at 230 C. What is the activation energy for this reaction? A. 6.17 x 10 3 kj/mol B. 31.4 kj/mol C. 78.2 kj/mol D. 124 kj/mol E. 163 kj/mol Go on to the next page
23. Suppose a certain biologically important reaction is quite slow at physiological temperature (37 o C) in the absence of a catalyst. Assuming that the collision factor A remains the same, by how much must an enzyme lower the activation energy of the reaction to achieve a million-fold increase (1 x 10 6 ) in the reaction rate? A. 10 kj/mol B. 36 kj/mol C. 51 kj/mol D. 74 kj/mol E. 82 kj/mol 24. The rate constant k for the reaction 3A 4B is 6.00 x 10 3 M 1 min 1. How long will it take for the concentration of A to drop from 0.75 M to 0.25 M? A. 2.2 x 10 3 min B. 5.5 x 10 3 min C. 180 min D. 440 min E. 5.0 x 10 2 min Go on to the last page
25. During a medical PET scan a patient is injected with a tracing compound that contains an 18 F isotope, which decays through positron emission. When the emitted positron encounters an electron both are completely destroyed through a matter-antimatter reaction, producing two photons that propagate in opposite directions. If the energy of each photon is 8.187 x 10 14 J, what is the mass of the positron? A. 2.174 x 10 4 amu B. 5.483 x 10 4 amu C. 2.097 x 10 3 amu D. 1.0072765 amu E. 1.0086649 amu END OF TEST
CHEM 112 SPRING 2013 EXAM 1 FORM - A SCRAP PAPER
CHEM 112 SPRING 2013 EXAM 1 FORM - A SCRAP PAPER
1. Standard Electrode Potentials Half-reaction E o 1/2(V) F 2 (g) + 2e 2F (aq) +2.87 H 2 O 2 (aq) + 2H + (aq) + 2e 2H 2 O() +1.78 Cl 2 (g) + 2e 2Cl (aq) +1.36 O 2 (g) + 4H + (aq) + 4e 2H 2 O() +1.23 Br 2 () + 2e 2Br (aq) +1.07 Ag + (aq) + e Ag(s) +0.80 Fe 3+ (aq) + e Fe 2+ (aq) +0.77 O 2 (g) + 2H + (aq) + 2e H 2 O 2 (aq) +0.68 I 2 (s) + 2e 2I (aq) +0.54 Cu + (aq) + e Cu(s) +0.52 Cu 2+ (aq) + 2e Cu(s) +0.34 Sn 4+ (aq) + 2e Sn 2+ (aq) +0.15 Cu 2+ (aq) + e Cu + (aq) +0.15 2H + (aq) + 2e H 2 (g) 0.00 Pb 2+ (aq) + 2e Pb(s) 0.13 Sn 2+ (aq) + 2e Sn(s) 0.14 Co +2 (aq) + 2e Co(s) 0.28 Ni 2+( aq) + 2e Ni(s) 0.28 Cd 2+ (aq) + 2e Cd(s) 0.40 Fe 2+ (aq) + 2e Fe(s) 0.44 Cr 3+ (aq) + 3e Cr(s) 0.74 Zn 2+ (aq) + 2e Zn(s) 0.76 2H 2 O() + 2e H 2 (g) + 2OH (aq) 0.83 SO 2 4 (aq) + H 2 O() + 2e SO 2 3 (aq) + 2OH (aq) 0.93 Mn 2+ (aq) + 2e Mn(s) 1.18 Al 3+ (aq) + 3e Al(s) 1.66 Mg 2+ (aq) + 2e Mg(s) 2.37 Na + (aq) + e Na(s) 2.71 Ca 2+ (aq) + 2e Ca(s) 2.76 Li + (aq) + e Li(s) 3.05 2. Constants R = 8.314 J mol 1 K 1 R = 0.0821 L-atm mol 1 K 1 F = 96,500 coulombs/mol electrons h = 6.62606876 x 10 34 J-s mass 1 0 n = 1.0086649 amu mass 1 1 p = 1.0072765 amu 1 g = 6.02 x 10 23 amu 1 amp = 1 coul sec 1 Avogadro s no. = 6.02214 x 10 23 mol 1 c = 2.99792458 x 10 8 m sec 1 1 J = kg m 2 sec 2 = C-V 3. Equations G = H T S = nfe Chem 112 Data Sheet G o = 2.303 RT log K = RT ln K G = G o + RT ln Q G = G o + 2.303 RT log Q E o = 0.0592 n log K (at 25 o C) E = E o 0.0592 log Q (at 25 o C) n [ X ] ph = pk a + log [ HX ] K a x K b = K w = [H + ] [OH ] pk w = ph + poh = pk a + pk b K p = K c (RT) Δn K w = 1 x 10 14 at 25 C ln k = ln k k 1 2 E a RT E a = R a k = Ae ( ) RT + ln A ln[a] = ln[a] o kt 1 [A] 1 [A] o t 1/2 = 0.693/k t 1/2 = 1/k[A] o 1 1 T 2 T kt 1 log ln N t = N o o N t = N 0.301t t 1 2 1 2 = kt 2.303 0.693t = kt k = t 4. MO Theory E Diagrams Rate = kn E = mc 2 0.693 t 1 2 E = hν c = λν 6. Crystal Field Splitting for octahedral complexes E d x2 y2, d z2 d xy, d yz, d xz email Δ o Name
PERIODIC TABLE of the ELEMENTS MAIN GROUPS MAIN GROUPS 1A 1 8A 18 1 H 1.008 2A 2 3A 13 4A 14 5A 15 6A 16 7A 17 2 He 4.003 3 Li 6.941 4 Be 9.012 TRANSITION METALS 5 B 10.811 6 C 12.011 7 N 14.007 8 O 15.999 9 F 18.998 10 Ne 20.180 11 Na 22.990 12 Mg 24.305 3B 3 4B 4 5B 5 6B 6 7B 7 8B 8 8B 9 8B 10 1B 11 2B 12 13 Al 26.982 14 Si 28.086 15 P 30.974 16 S 32.066 17 Cl 35.453 18 Ar 39.948 19 K 39.098 20 Ca 40.078 21 Sc 44.956 22 Ti 47.867 23 V 50.942 24 Cr 51.996 25 Mn 54.938 26 Fe 55.845 27 Co 58.933 28 Ni 58.693 29 Cu 63.546 30 Zn 65.39 31 Ga 69.723 32 Ge 72.61 33 As 74.992 34 Se 78.96 35 Br 79.904 36 Kr 83.80 37 Rb 85.468 38 Sr 87.62 39 Y 88.906 40 Zr 91.224 41 Nb 92.906 42 Mo 95.94 43 Tc [98] 44 Ru 101.07 45 Rh 102.90 46 Pd 106.42 47 Ag 107.87 48 Cd 112.41 49 In 114.82 50 Sn 118.71 51 Sb 121.76 52 Te 127.60 53 I 126.90 54 Xe 131.29 55 Cs 132.91 56 Ba 137.33 57 La* 138.91 72 Hf 178.49 73 Ta 180.95 74 W 183.84 75 Re 186.21 76 Os 190.23 77 Ir 192.22 78 Pt 195.08 79 Au 196.97 80 Hg 200.59 81 Tl 204.38 82 Pb 207.2 83 Bi 208.98 84 Po [209] 85 At [210] 86 Rn [222] 87 Fr [223] 88 Ra [226] 89 Ac** [227] 104 Rf [261] 105 Db [262] 106 Sg [266] 107 Bh [264] 108 Hs [265] 109 Mt [268] 110 [269] 111 [272] 112 [277] 114 [285] 116 [289] 118 [293] * LANTHANOIDS 58 Ce 140.12 59 Pr 140.91 60 Nd 144.24 61 Pm [145] 62 Sm 150.36 63 Eu 151.96 64 Gd 157.25 65 Tb 158.92 66 Dy 162.50 67 Ho 164.93 68 Er 167.26 69 Tm 168.93 70 Yb 173.04 71 Lu 174.97 ** ACTINOIDS 90 Th 232.04 91 Pa 231.04 92 U 238.03 93 Np [237] 94 Pu [244] 95 Am [243] 96 Cm [247] 97 Bk [247] 98 Cf [251] 99 Es [252] 100 Fm [257] 101 Md [258] 102 No [259] 103 Lr [262]