DO NOT OPEN THE EXAM UNTIL THE PROCTOR TELLS YOU TO DO SO

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1 CHEM 1021, Spring 2000 Exam #2 March 15, 2000 Prof. J. T. Roberts DO NOT OPEN THE EXAM UNTIL THE PROCTOR TELLS YOU TO DO SO Instructions: 1. Fill in the bubble sheet with your name (last name first), ID number, and test version. (This is version A). Use a soft lead pencil to do this. This information must be entered correctly, or your test will not be scored properly. 2. Write the special code that is printed on your bubble sheet here: my code for Exam 2 is. This is a unique code for your test. Test results will be posted by this number only on the class web page. 3. There are 20 multiple choice questions. Mark the letter (a-e) on your answer bubble sheet of the one choice that best answers the question. There is no partial credit, and you need not show your work. Use scratch paper or the backs of the exam pages if you need space to work. 4. You are permitted to have one sheet of paper containing any information you wish written or printed on both sides. There is a periodic table attached to the back of the exam. 5. You must remain seated until the exam is officially over. All answer sheets will be collected at the same time. Hand in the answer sheet only. Keep your copy of the exam for self-scoring and review. 6. The answer key will be available on the class home page ( by tomorrow afternoon. Test results will be posted on the class web page by next Monday afternoon. Some important constants and equations that you may need: R = J / mol K = L atm / mol K (R = gas constant) h = J s -1 (h = Planck s constant) c = m s -1 (c = speed of light) 1 nm = 10-9 m 1 ml = 1cm 3 = 10-3 L K = ºC P V = n R T (ideal gas equation) P total = P 1 + P 2 + P 3 + (Dalton s law) u rms = (3 R T / M) 1/2 (root mean square speed) E system = q system + w system (conservation of energy) E = J (Z 2 / n 2 ) (Bohr atom) E photon = h c / λ

2 Page 2 1. At 200 K, the molecules or atoms of an unknown gas, X, have an average velocity equal to that of Ar atoms at 400 K. What is X? (Assume ideal gas behavior.) (a) He (b) CO (c) HF (d) HBr (e) F 2 2. Which of the following statements about quantum theory is not correct? (a) The energy and position of an electron cannot be determined simultaneously. (b) Lower energy orbitals are filled with electrons before higher energy orbitals. (c) When filling orbitals of equal energy, two electrons will occupy the same orbital before filling a new orbital. (d) No two electrons in the same atom can have the same four quantum numbers. (e) All of these is correct. 3. For a particular process, q system = 20 kj and w system = 15 kj. Which of the following statements is true? (a) The direction of energy flow as heat is from system to surroundings. (b) The direction of energy flow as work is from system to surroundings. (c) E system = 35 kj. (d) All of the above statements are true. (e) None of the above statements are true.

3 Page ml of pure water at K is mixed with 50.0 ml of pure water at K. What is the final temperature of the water, assuming that they are mixed in a perfect calorimeter? (a) K (b) K (c) K (d) K (e) K 5. At 25 ºC, the following standard state enthalpies of reaction are known: 2 ClF (g) + O 2 (g) Cl 2 O (g) + F 2 O (g) Hº = kj 2 ClF 3 (g) + 2 O 2 (g) Cl 2 O (g) + 3 F 2 O (g) Hº = kj 2 F 2 (g) + O 2 (g) 2 F 2 O (g) Hº = kj At the same temperature, calculate Hº for the reaction: ClF (g) + F 2 (g) ClF 3 (g) Hº =? (a) kj (b) kj (c) kj (d) kj (e) None of these answers are correct. 6. Of the following elements, which has the lowest first ionization energy? (a) O (b) Li (c) N (d) Be (e) K

4 7. What is the energy of a photon of blue light that has a wavelength of 450 nm? (a) J (b) J (c) J (d) J (e) J Exam #2 Page J of energy are required to raise the temperature of 15 g of gold by 25 ºC at a constant pressure of 1 atm. What is the constant pressure heat capacity of gold? -1 (a) 29 J g -1 ºC -1 (b) 0.13 J g -1 ºC -1 (c) 79 J g -1 ºC -1 (d) J g -1 ºC (e) none of these 9. The van der Waals equation, n R T = [P + (n 2 a / V 2 )] (V - n b), incorporates corrections to the ideal gas law in order to account for the properties of real gases. One of the corrections accounts for: (a) the possibility of chemical reactions between molecules. (b) the finite volume of molecules. (c) the quantum behavior of molecules. (d) the fact that average kinetic energy is inversely proportional to temperature. (e) the possibility of phase changes when the temperature is decreased or the pressure is increased.

5 Page All of the following statements about the greenhouse effect are true except: (a) The molecules H 2 O and CO 2 play an important role in retaining the atmosphere s heat. (b) Low humidity levels in the atmosphere allow efficient radiation of heat back into space. (c) The carbon dioxide content of the atmosphere has been stable for the past 100 years. (d) Deserts become cold on summer nights partly because of the greenhouse effect. (e) Most of the water vapor in the atmosphere is derived from evaporation from natural sources such as rivers, lakes, and oceans. 11. How many electrons in an atom can have the quantum numbers n = 4 and l = 2? (a) 14 (b) 12 (c) 10 (d) 6 (e) In the gas phase, which of the following molecules would be the most polar? (a) CsF (b) CsCl (c) NaCl (d) NaF (e) LiF

6 13. A carbon dioxde laser produces radiation with a wavelength of m. A particular carbon dioxide laser puts out a pulse of light in which the total energy output is J How many photons are produced in this pulse? (a) (b) (c) (d) (e) Exam #2 Page Which of the following statements about hydrogen are true? I. H has a smaller first ionization energy than He. II. H - is smaller than H. III. H bonds with halogens to form polar covalent compounds. IV. H is always a metal. V. H does not have a second ionization energy. (a) I, V (b) II, IV (c) I, III, V (d) II, IV, V (e) I, III, IV, V

7 Page In Experiment 6, you used a black light to investigate what happens when certain objects are irradiated in the UV-A wavelength region. What is the best explanation for why certain objects appear especially white and bright when they are irradiated with UV-A? (a) The UV-A radiation raises electrons in some molecules to high energy states, which then release some of their energy as visible light. (b) Irradiation by a black light heats an object, thereby causing it to emit white light. (c) The black light initiates chemical reactions which result in the emission of light. (d) The UV-A ionizes a small fraction of the atoms in an object, thereby causing the objects to emit light. (e) The black light filters out reflected visible light from the room, making photons in the white and bright wavelength region easy to detect. 16. The ground electron configuration of copper (Cu) is: (a) [Ar]4s 2 3d 9 (b) [Kr]4s 2 3d 9 (c) [Ar]4s 1 3d 10 (d) [Ar]4s 2 4d 9 (e) [Ar]3s 1 3d Which of the following molecules or ions has a non-zero dipole moment? (a) CO 2 (linear molecule with two identical bonds) (b) CO 2-3 (planar molecule with three identical bonds 120º apart) (c) NH + 4 (tetrahedral molecule with four identical bonds 109.5º apart) (d) PF 3 (pyramidal molecule with three identical P-F bonds; like NH 3 ) (e) Two of the above-listed molecules have non-zero dipole moments.

8 Page The total volume of hydrogen gas needed to fill the Hindenburg blimp was L at 1.00 atm and 25.0 ºC. How much energy was evolved when it burned, assuming that O 2 was in excess? The relevant reaction is shown below. 1 H2 (g) + O2 (g) H2 O 2 (l) H = -286 kj (a) kj (b) kj (c) kj (d) kj (e) kj 19. A ml sample of gas is collected over water at 22.0 ºC and torr total pressure. What is the volume of dry gas at 0.0 ºC and 760 torr pressure? The vapor pressure of water at 22.0 ºC is 20.0 torr. Assume ideal gas behavior. (a) 146 ml (b) 136 ml (c) 126 ml (d) 116 ml (e) none of the above 20. Which of the following statements about the troposphere is false? (a) Only astronauts have ventured beyond the troposphere. (b) The temperature of the troposphere usually decreases with altitude. (c) Gases readily move between the upper and lower troposphere. (d) Most naturally occurring chlorine in the upper troposphere is derived from salt in sea water. (e) Tropospheric winds are the result of pressure differences and planetary motion.

9 ANSWER KEY FOR EXAM 2, VERSION A 1. (c) 11. (c) 2. (c) 12. (a) 3. (c) 13. (e) 4. (b) 14. (c) 5. (d) 15. (a) 6. (e) 16. (c) 7. (b) 17. (d) 8. (b) 18. (d) 9. (b) 19. (d) 10. (c) 20. (d)