Microsoft Word - Practice Exam 2 Workout Problems .docx Practice EXAM 2 Workout Problems r = !"($%&$)( ) r = !*($%&$) ( ) r = $%&$ * WORKOUT PROBLEMS. SHOW ALL OF YOUR WORK Tungsten (W) crystallizes...

Chemistry 2 exam 20 questions 18 multiple choice, 2 work out problems showing work is not required


Microsoft Word - Practice Exam 2 Workout Problems .docx Practice EXAM 2 Workout Problems r = !"($%&$)( ) r = !*($%&$) ( ) r = $%&$ * WORKOUT PROBLEMS. SHOW ALL OF YOUR WORK Tungsten (W) crystallizes in a body-centered cubic unit cell and has an atomic radius of 137 pm. a) Calculate the edge length (in picometers) of a unit cell in this crystal. b) Calculate the density of tungsten (in g/mL). For the overall reaction shown below, it was found that when compound A was doubled, the rate doubled. The rate constant was found to be 0.0067 s-1 Overall reaction: A à products a) Write the experimentally determined rate law for this reaction. b) Calculate the final concentration of compound A if [A]0 = 0.425 M and the reaction was allowed to run for 2.35 minutes. c) When the reaction temperature was increased from 15.0 0C to 37.0 0C, the rate of this reaction increased by a factor of 6. Calculate the activation energy (in kJ/mol) for the rate-determining step of this reaction. 1 Chem 1110 Practice Exam 2 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. In the cesium chloride unit cell shown below, the cesium ions sit on the corners of a cube. What is the name of this unit cell? a. simple cubic d. cubic-centered b. chloride-centered cubic e. body-centered cubic c. face-centered cubic 2. Which of the following unit cells has the highest packing efficiency? a. simple cubic b. face-centered cubic c. body-centered cubic d. both face-centered and body-centered cubic e. Simple, face-centered, and body-centered cubic all have the same packing efficiency. 3. Silver crystallizes with a face-centered cubic unit cell. The edge length is 407.7 pm. What is the volume of this unit cell? a. 7.68 x 107 pm3 d. 9.87 x 107 pm3 b. 6.78 x 107 pm3 e. 3.88 x 107 pm3 c. 8.67 x 107 pm3 4. One reaction that occurs in an automobile catalytic converter is the conversion of carbon monoxide to carbon dioxide. How could the rate of this reaction be expressed correctly in terms of the rate at which the concentration of a reactant or product changes? 2CO(g) + O2(g) → 2CO2(g) a. Rate = Δ[CO]/Δt d. Rate = – Δ[CO]/Δt b. Rate = –Δ[CO]/Δt e. Rate = 2Δ[CO2]/Δt c. Rate = Δ[O2]/Δt Name: ______________________ 2 5. The following graph shows the kinetics curves for the reaction of oxygen with hydrogen to form water: O2(g) + 2H2(g) → 2H2O(g). Which curve is hydrogen? a. the dashed curve b. the gray curve c. the black curve d. either the gray or the black curve e. Any of these curves could be hydrogen. 6. If the rate of formation of ammonia is 0.345 M/s, what is the rate of disappearance of N2? N2(g) + 3H2(g) → 2NH3(g) a. 0.173 M/s d. 245 M/s b. 0.345 M/s e. 0.518 M/s c. 0.690 M/s 7. Which of these could be the units for the rate constant in a second-order reaction? a. M–1 s d. M– 2 s– 1 b. M s– 1 e. Ms c. M– 1 s– 1 8. A reaction is first order in A. If the rate constant of the reaction is 3.45 × 10– 3 s– 1, what is the half-life (t1/2) of the reaction? a. 4.98 × 10– 3 s d. 100 s b. 200 s e. 1.73 × 10– 3 s c. 3.45 × 10– 3 s 9. The reaction CHCl3(g) + Cl2(g) → CCl4(g) + HCl(g) has the following rate law: Rate = k[CHCl3][Cl2]. If the concentration of CHCl3 is increased by a factor of five while the concentration of Cl2 is kept the same, the rate will ________ a. double. d. increase by a factor of five. b. triple. e. decrease by a factor of one-fifth. c. stay the same. Name: ______________________ 3 10. Given the following data, determine the rate law for the reaction NH4+(aq) + NO2–(aq) → N2(g) + 2H2O(l) Experiment [NH4+] (M) [NO2–] (M) Rate (M/s) 1 0.2500 0.2500 1.25 × 10– 3 2 0.5000 0.2500 2.50 × 10– 3 3 0.2500 0.1250 6.25 × 10– 4 a. k[NH4+][NO2–] d. k[NH4+]1/2[NO2–]2 b. k[NH4+]2[NO2–] e. k[NH4+][NO2–]2 c. k[NH4+][NO2–]1/2 11. Which of the following plots would indicate that a reaction was first order? a. c. b. d. 12. Chlorine dioxide (ClO2) is used as a disinfectant in municipal water-treatment plants. It decomposes in a first-order reaction with a rate constant of 0.0714 s– 1. If the initial concentration were 0.12 M, what would the concentration be after 14.0 s has elapsed? a. 0.033 M d. 0.012 M b. 0.12 M e. 0.044 M c. 0.060 M Name: ______________________ 4 13. Which point as labeled by an asterisk (*) on the following energy profile is the transition state? a. c. b. d. 14. The reaction NO2(g) + CO(g) → NO(g) + CO2(g) is thought to occur by the following mechanism: Step 1: NO2(g) + NO2(g) → NO3(g) + NO(g) Step 2: NO3(g) + CO(g) → NO2(g) + CO2(g) Which of the following species is an intermediate? a. NO2 b. NO c. NO3 d. CO2 e. This mechanism has no intermediates. 15. A proposed mechanism for the decomposition of ozone in the stratosphere is: Step 1: Cl(g) + O3(g) → ClO(g) + O2(g) Step 2: ClO(g) + O3(g) → Cl(g) + 2 O2(g) What is the molecularity of step 2? a. unimolecular b. bimolecular c. termolecular d. zero molecular (spontaneous) e. More information is needed to answer this question. Name: ______________________ 5 16. What is the predicted rate law for the following mechanism for the reduction of nitrogen in NO by hydrogen? Step 1: H2(g) + 2 NO(g) → N2O(g) + H2O(g) (slow) Step 2: N2O(g) + H2(g) → N2(g) + H2O(g) (fast) What is the rate law? a. Rate = k[H2][NO] b. Rate = k[H2]2[NO] c. Rate = k[H2][NO]2 d. Rate = k[H2]2[NO]2 e. More information is needed to answer this question. 17. The mechanism for the first-order reaction 2H2O2(aq) → 2H2O(l) + O2 in the presence of I–(aq) is proposed to be: Step 1: H2O2(aq) + I–(aq) → H2O( ) + OI–(aq) (slow) Step 2: H2O2(aq) + OI–(aq) → H2O( ) + O2(g) + I–(aq) (fast) Identify the catalyst in the reaction. a. H2O2 d. H2O b. OI– e. O2 c. I– 1 Chem 1110 Practice Exam 2 Answer Section MULTIPLE CHOICE 1. ANS: E 2. ANS: B 3. ANS: B 4. ANS: D 5. ANS: C 6. ANS: A 7. ANS: C 8. ANS: B 9. ANS: D 10. ANS: A 11. ANS: C 12. ANS: E 13. ANS: C 14. ANS: C 2 15. ANS: B 16. ANS: C 17. ANS: C