Chemistry 1210, Section 1 Second Hour Exam October 26, 2011 Instructions: Do not begin until 8:30 AM. The exam must be turned in by 9:20 AM. This exam should have 25 questions. Each question is worth 4 points for a total of 100 points. A periodic table should be on the next page. Use only a #2 Pencil to mark the best answer on the ScanTron Sheet. Fill out the scantron completely. You will turn in only the Scantron sheet. You should keep the rest of the exam. Please present your student activity card or other form of identification when turning in the exam. Please do not spend too much time on any one problem. If you get stuck, move on to an easier problem, and come back to the harder one later. Good luck! Information: Constants: Av. number = 6.022 x 10 23 h = 6.626 x 10-34 J s c = 3.00 x 10 8 m/s R H = 2.18 x 10-18 J Conversion factors: 1 inch = 2.54 cm 1 J = 1 kg m 2 /s 2 1 Hz = 1 s -1 R H = 2.18 x 10-18 J Equations: d = m/v M1V1 = M2V2 H = H final -H initial H rxn = Σ n H f (products) - Σ m H f (reactants) specific heat q mass ΔT 2 = E k = mv λυ = c λ = h/mv E = q + w E = hυ E = nhυ 1 2 E 1 1 1 = (-RH )( ) ΔE = (RH )( ) = hν 2 2 n ni n f n 2 Z eff = Z S Formulas and names of common polyatomic ions: 2-2- Carbonate ion = CO 3 Sulfate ion = SO 4 - - Nitrate ion = NO 3 Perchlorate ion = ClO 4 3- + Phosphate ion = PO 4 Ammonium ion = NH 4 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 14 6s 2 6p 6 6d 10 6f 14 Periodic table here.
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3 1. A chemical reaction in which the system gains heat from the surroundings is said to be (i) and has a (ii) value of ΔH, while a chemical reaction in which the system releases heat to the surroundings is said to be (iii) and has a (iv) value of ΔH (i) (ii) (iii) (iv) a. exothermic negative endothermic negative b. endothermic negative exothermic positive c. exothermic positive endothermic negative d. exothermic negative endothermic positive e. endothermic positive exothermic negative 2. Calculate the change in internal energy of the system for a chemical reaction in which 10.0 kj of heat is absorbed by the system and the system does 15.0 kj of work on the surroundings. a. -5.0 kj b. -25.0 kj c. +5.0 kj d. +25.0 kj e. +15.0 kj 3. Of the following, which are correctly referred to as state functions? (i) calories burned in a 20 minute workout (ii) straight line distance from Salt Lake City to Logan (iii) amount of work performed in the combustion of a gallon of gasoline (iv) the heat change for a chemical reaction carried out at constant pressure (v) number of students currently in this room a. all of the above are state functions b. (ii) and (v) only c. (ii), (iii), (iv), and (v) only d. (ii), (iv), and (v) only e. (ii), (iii), (iv), and (v) only 4. Nitrogen and oxygen can be combined to produce nitrogen dioxide according to the following balanced chemical equation: N 2 (g) + 2 O 2 (g) 2 NO 2 (g) ΔH =? kj Under standard conditions, the reaction of 10.00 grams of O 2 with excess N 2 to produce NO 2 was found to require the input of 10.37 kj of heat. Use this information to determine the enthalpy change associated with this reaction. a. 33.18 kj b. 66.36 kj c. 16.59 kj d. 10.23 kj e. 5.116 kj 5. Given the data below, determine ΔH for the reaction: 2 C (s) + O 2(g) 2 CO (g)
C (s) + O 2(g) CO 2(g) ΔH = -393.5 kj 4 CO (g) + ½ O 2(g) CO 2 (g) ΔH = -283.0 kj a. -22l.0 kj b. -110.5 kj c. +110.5 kj d. +221.0 kj e. -676.5 kj 6. Instant ice packs make use of an endothermic chemical reaction wherein ammonium nitrate, NH 4 NO 3 dissolves in water according to the following equation: NH 4 NO 3 (s) NH 4 + (aq) +NO 3 - (aq) ΔH =? kj When 0.100 mol of NH 4 NO 3 is dissolved in a total solution volume of 50.0 ml in a calorimeter, the temperature decreases from 27.00 C to 14.70 C. Use this information to determine the enthalpy change for NH 4 NO 3 dissolving in water in units of kj/mol of reaction. Assume the specific heat of the solution is the same as that of pure water (4.18 J/g C ) and that the density of the solution is 1.00 g/ml. a. +17.0 kj b. +10.3 kj c. +25.7 kj d. +0.257 kj e. +0.170 kj 7. Use the following standard enthalpy of formation data to calculate H for the following reaction: 3 Fe 2 O 3 (s) + H 2 (g) 2 Fe 3 O 4 (s) + H 2 O(g) ΔH =? kj compound o Δ H f Fe 2 O 3 (s) -824.2 Fe 3 O 4 (s) -1118.4 H 2 O (g) -241.8 a. -536 kj b. -4951 kj c. -2184 kj d. -3349 kj e. -6.00 kj (kj/mol)
8. According to the first law of thermodynamics: a. the energy of the surroundings increases for any chemical reaction b. enthalpy is a state function c. internal energy is a state function d. the energy of the universe is constant e. both (a) and (d) are correct 5 9. For radiant energy, a higher energy is associated with a i) frequency and (ii) wavelength (i) (ii) a. higher longer b. lower shorter c. lower longer d. higher shorter 10. Chlorophyll a is a light absorbing pigment in plants that is important in photosynthesis. The wavelength of light that chlorophyll a absorbs maximally is 430 nm. What is the frequency of this light in Hz? a. 1.29 10 20 b. 6.98 10 14 c. 1.29 10 2 d. 1.43 10-15 e. 1.43 10 3 11. Solar panels can be used to charge lead-acid batteries of the type found in your car. Suppose you have a fully discharged battery that requires 3,177 kj of energy to charge completely. Now suppose you use the light energy from a green laser light that has a frequency of 5.64 x 10 14 s -1 to charge the battery using a solar panel. How many photons of green laser light must be absorbed by the solar panel to fully charge the battery, assuming the process is 100% efficient? a. 8.50 x 10 24 b. 2.70 x 10 54 c. 1.19 x 10-12 d. 8.50 x 10 21 e. 2.70 x 10 51
12. For the 4d yz orbital, the "yz" specifies the orbital s: a. size b. shape c. orientation in space d. electron spin e. energy state 6 13. Which of the following is a correct statement of Einstein s interpretation of the photoelectric effect? a. the energy states of electrons are quantized b. matter in motion has a wavelength c. radiant energy has particle like properties d. only certain energies can be released when electrons undergo transitions between energy states e. more than one of the above correctly summarizes Einstein s interpretation of the photoelectric effect 14. How much energy is required to promote an electron in the hydrogen atom from the n = 2 state to the n = 5 state? a. 3.37 x 10-19 J b. 4.84 x 10-19 J c. 4.57 x 10-17 J d. 4.57 x 10-19 J e. 6.54 x 10-18 J 15. How many orbitals are present in the (i) n = 2, (ii) n = 3 and (iii) n = 4 shells? (i) (ii) (iii) a. 3 9 16 b. 6 18 32 c. 4 6 8 d. 4 9 16 e. 8 18 32 16. For the following orbital drawings, which represents a violation of Hund s rule? a. b. c. d. e. more than one of the above violate Hund s rule
17. The Heisenberg Uncertainty Principle states that it is impossible to precisely predict which two properties of an electron in an atom (a) orientation and energy state (b) electron spin and orbital (c) wavelength and velocity (d) shape and orientation (e) momentum and position 7 18. How many unpaired electrons are present in the ground state of the element Ruthenium (Ru)? a. 1 b. 2 c. 3 d. 4 e. 5 19. Which of following will have the longest debroglie wavelength? a. a helium nucleus moving at 1000 m/s b. a helium nucleus moving at 10,000 m/s c. a neutron moving at 1000 m/s d. an electron moving at 1000 m/s e. an electron moving at 10 6 m/s 20. Atomic radius generally increases moving. a. down a group and from right to left across a period b. up a group and from right to left across a period c. down a group and from left to right across a period d. up a group and from left to right across a period 21. Based on what we discussed in class, which of the following atoms is most likely to violate the general trend observed for electron affinity when moving from left to right within row 3 of the periodic table? a. Mg and S b. Mg and P c. Al and S d. Al and P e. P and S
22. Based on what we discussed in class, which of the following atoms is most likely to violate the general trend observed for ionization energy when moving from left to right within row 3 of the periodic table? a. Mg and S b. Mg and P c. Al and S d. Al and P e. P and S 8 23. Which of the following atom would be predicted to have a fourth-ionization energy very much greater than the third? a. Na b. Mg c. Al d. Si e. P 24. What is the effective nuclear charge (Z eff ) felt by the valence electrons of Cl? a. 3 b. 5 c. 6 d. 7 e. 8 25. Which of the following would you predict would have the most negative electron affinity? a. Se b. Ar c. Cl d. Na e. K