Chem 1202-3 Fall 2023 Exam 2, Form 2 PDF

CHEM 1202-3 Fall 2023, Dr. Ngo Exam 2, Form 2 PRINT your name: __________________________________________ Instructions: Use 8.5 x 11 inch scantron. On SIDE TWO of the scantron 1. Print you LAST NAME, then FIRST NAME a...

CHEM 1202-3 Fall 2023, Dr. Ngo Exam 2, Form 2 PRINT your name: __________________________________________ Instructions: Use 8.5 x 11 inch scantron. On SIDE TWO of the scantron 1. Print you LAST NAME, then FIRST NAME and bubble it in 2. Bubble in your complete, correct LSU ID (89-xxx-xxxx) and name. 3. Bubble 2 under Grade or Education on the scantron sheet. On SIDE ONE of the scantron 1. Print your name 2. Answers to the exam questions must go on side one. Bubble the answers on the scantron sheet using a pencil. 3. There is exactly one best answer for each question, and you should NOT leave a question blank. 4. On a numerical question, choose the response closest to the correct answer This exam is closed notes and closed book. You are not allowed to use your own scratch paper. Only a scientific calculator is allowed during the exam, NO graphing calculators. Mark your answers in your Exam for future reference. You can keep your Exam for further study Present your LSU ID and the front of your exam when submitting your scantron. 1 Useful Info: The periodic table is located at the back of the exam booklet. Useful constants and select formulas J L R = 8.314 = 0.08206 atm ∙ 101.3 J = 1 L ∙ atm mol ∙ K mol o o o q ΔGrxn = ΔHrxn − TΔSrxn ΔE = q + w ΔS = T o o −ΔG⬚ ΔG = ΔG⬚ + RT(ln Q) K eq = exp ( ) RT q Cs = q = −Ccal × ΔT m × ΔT 2 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1. Which of the reactions produces an increase in the entropy of the system? A. 3 NO2 (g) + H2O (l) ⟶ 2 HNO3 (aq) + NO (g) B. CCl4 (l) + 4 HCl (g) ⟶ CH4 (g) + 4 Cl2 (g) C. 2 NO (g) + O2 (g) ⟶ 2 NO2 (g) D. C6H6 (l) + 3 H2 (g) ⟶ C6H12 (l) E. Mg (s) + 2 Cl2 (g) ⟶ MgCl2 (s) 2. Which of the following compound will NOT have ∆Hof = 0 kJ/mol? A. Cl2 (g) B. O2 (g) C. Na (s) D. I2 (s) E. PbSO4 (s) 3. When 7.00 g of solid sodium hydroxide, NaOH, is dissolved in 100.0 g of water in a coffee-cup calorimeter (see the picture on the right), the temperature rises from 25.00oC to 85.66oC. Calculate ΔH in kJ/mol of NaOH for the process. The specific of water is 4.184 J/g-C. Molar mass of NaOH is 39.997 g/mol A. ΔH = 27.2 kJ/mol B. ΔH = 532.1 kJ/mol C. ΔH = 185.7 kJ/mol D. ΔH = –155.2 kJ/mol E. ΔH = –73.3 kJ/mol 3 4. A fuel is burned in a cylinder equipped with a piston. The initial volume of the cylinder is 30.0 L, and the final volume is 80.0 L. If the piston compresses against a constant pressure of 2.50 atm, how much work (in kJ) is done? (1 L-atm = 101.3 J) A. –12.5 kJ B. –12.7 kJ C. –21.1 kJ D. 6.63 kJ E. 7.25 kJ 5. Consider the following reaction: CaC2 (s) + 2 H2O (l) ⇋ Ca(OH)2 (aq) + C2H2 (g) If 15.0 g of CaC2 reacts with water at standard conditions, how much heat (in kJ) is released by the reaction? ΔHof of the reaction is –141.7 kJ/mol. Molar mass of CaC2 is 64.1 g/mol. A. –47.5 kJ B. –7.84 kJ C. –390.1 kJ D. –41.6 kJ E. –33.2 kJ 6. Choose the process from below which describes a change which is dependent of the path by which the change occurs. Read each statement carefully. A. The amount of work required to build a house. B. The heat released by the combustion of one liter of gasoline. C. The number of rotations the earth undergoes over a specified period. D. The potential energy gained by a satellite as it is shot into a specific orbit. E. The elevation-increase experienced by a person who travels from Louisiana to Alaska. 4 7. How much heat (in kJ) is needed to raise the temperature of 5.00 kg of an Aluminum cube from 100.0oC to 600oC? The specific of aluminum is 0.89 J/g-C A. 6235 kJ of heat is needed. B. 322 kJ of heat is needed. C. 1024 kJ of heat is needed. D. 2225 kJ of heat is needed. E. 897 kJ of heat is needed. 8. Elemental mercury, Hg, is a silver liquid at room temperature. Its normal freezing point if –38.9oC, and its enthalpy of fusion, ΔHfusion, is 2.29 kJ/mol. What is the change in entropy in the system when 75.0 g of liquid mercury freezes at the normal freezing point? Molar mass of mercury is 200.59 g/mol A. ΔS = 23.5 J/mol-K B. ΔS = 7.59 J/mol-K C. ΔS = 5.62 J/mol-K D. ΔS = –24.4 J/mol-K E. ΔS = –3.66 J/mol-K 9. Calculate ∆E and determine whether the process is endothermic or exothermic for the following case: A system releases 832 kJ of heat to the surroundings and does 18 kJ of work on the surroundings. A. ∆E = 814 kJ. This process is exothermic B. ∆E = 617 kJ. This process is endothermic C. ∆E = –589 kJ. This process is exothermic. D. ∆E = –90 kJ. This process is endothermic. E. ∆E = –850 kJ. This process is exothermic. 5 The following reaction and thermodynamic data are to be used for questions 10 and 11 Fe2O3 (s) ∆Hof = –822.16 kJ/mol So = 89.96 J/mol ∆Gof = –740.98 kJ/mol HCl (g) ∆Hof = –92.30 kJ/mol So = 186.69 J/mol ∆Gof = –95.27 kJ/mol FeCl3 (s) ∆Hof = –400 kJ/mol So = 142.3 J/mol ∆Gof = –334 kJ/mol H2O (g) ∆Hof = –241.82 kJ/mol So = 188.83 J/mol ∆Gof = –228.57 kJ/mol Fe2O3 (s) + 6 HCl (g) ⇋ 2 FeCl3 (s) + 3 H2O (g) 10. Calculate ∆Horxn for the reaction above at 298 K. Pick the choice which gives this ∆Horxn value. A. ∆Horxn = 104.8 kJ/mol B. ∆Horxn = 156.3 kJ/mol C. ∆Horxn = –276.2 kJ/mol D. ∆Horxn = –149.5 kJ/mol E. ∆Horxn = –912.1 kJ/mol 11. ∆Gorxn for the reaction above is –41.1 kJ/mol at 298 K. Why there is a difference between ∆Horxn value and ∆Gorxn? Pick the best statement that gives the best reasoning. A. Because the energy difference is going into the ∆Sorxn B. Because the system is absorbing the energy difference. C. Because some of the energy is given off as light, not heat. D. Because the surroundings are absorbing the energy difference. E. Because there is an element in its natural state as one of the reactants. 6 12. Which of the following statements about enthalpy is TRUE? A. Because enthalpy relates to heat, the enthalpy change for a process will depend on the path taken. B. The enthalpy of a reaction is not the same as the heat of the reaction. C. A process for which ΔH > 0 is called endothermic. D. A positive ΔH corresponds to an exothermic process. E. When pressure is not constant, the change in enthalpy of a process is equal to the amount of heat transferred into or out of the system 13. Consider the following reaction: PbS (s) + 4 H2O2 (aq) ⇋ PbSO4 (s) + 4 H2O (l) Which of the following describes correctly how ΔG of this reaction changes when a particular substance is added to or removed from the reaction? A. Adding PbSO4 (s) to the reaction decreases the value of ∆G. B. Adding H2O2 (aq) to the reaction increases the value of ∆G. C. Removing PbSO4 (s) from the reaction increases the value of ∆G. D. Removing H2O2 (aq) from the reaction increases the value of ∆G. E. Removing PbS (s) from the reaction increases the value of ∆G. 14. Consider the following reaction: BaSO4 (s) ⇋ Ba2+ (aq) + SO42- (aq) What is the concentration of Ba2+ (aq) if enough Na2SO4 is added to raise the SO42- (aq) concentration to 2.5 M? Ksp of BaSO4 is 1.1 × 10-10 at 25oC A. [Ba2+] = 4.40 × 10-11 M B. [Ba2+] = 2.05 × 10-5 M C. [Ba2+] = 1.97 × 10-10 M D. [Ba2+] = 7.23 × 10-7 M E. [Ba2+] = 3.08 × 10-3 M 7 15. Consider the following data: H2 (g) + F2 (g) ⇌ 2 HF (g) ΔHo = –537 kJ CF4 (g) ⇌ C (s) + 2 F2 (g) ΔHo = 680 kJ 2 C (s) + 2 H2 (g) ⇌ C2H4 (g) ΔHo = 52.3 kJ Use Hess’s law to calculate ΔHo for the reaction below. Pick the choice which gives this ΔHo value C2H4 (g) + 6 F2 (g) ⇌ 2 CF4 (g) + 4 HF (g) A. ΔHo = –1164.7 kJ/mol B. ΔHo = –2486.3 kJ/mol C. ΔHo = 513.5 kJ/mol D. ΔHo = 195.3 kJ/mol E. ΔHo = 90.7 kJ/mol 16. Consider the following thermodynamic data: MgO (s) ∆Hof = –601.8 kJ/mol So = 26.8 J/mol Mg (s) ∆Hof = 0 kJ/mol So = 32.51 J/mol O2 (g) ∆Hof = 0 kJ/mol So = 205.0 J/mol Assume that ∆Ho and ∆So do not change much with temperature. Calculate the temperature where the reaction below would be spontaneous. Pick the choice which gives this temperature value. 2 MgO (s) ⇋ 2 Mg (s) + O2 (g) A. Above 5561 K, the reaction will be spontaneous. B. Above 500 K, the reaction will be spontaneous. C. Below 5300 K, the reaction will be spontaneous. D. Below 1206 K, the reaction will be spontaneous. E. Below 2614 K, the reaction will be spontaneous. 8 17. Which of the following molecules has the lowest absolute entropy? A. AlN (s) B. HCl (g) C. N2O4 (g) D. TiCl4 (l) E. C2H5OH (g) 18. Consider the following reaction: NO2 (g) + N2O (g) ⇋ 3 NO (g) The change in enthalpy at 298 K for this reaction is ∆Horxn = 155.67 kJ/mol. Under the same conditions, the entropy change for this reaction is ∆Sorxn = 171.41 J/mol-K. Calculate the value of Keq for this reaction at 2000 K. Assume that ∆Horxn and ∆Sorxn are the same and do not change with temperature. Use R = 8.314 J/K for the value of the gas constant A. At this temperature, Keq = 3.66 x 10-5 B. At this temperature, Keq = 1.86 x 10-10 C. At this temperature, Keq = 7.73 x 104 D. At this temperature, Keq = 1.64 x 105 E. At this temperature, Keq = 5.62 x 10-7 19. Which of the following statements about spontaneous processes is FALSE? A. A spontaneous process is irreversible. B. A process for which ΔG < 0 is called spontaneous. C. A spontaneous process can proceed on its own, regardless of speed. D. A process that is spontaneous will proceed without an energy input. E. Processes that are spontaneous in one direction are also spontaneous in the opposite direction. 9 20. Consider the following process: Natural gas is burned, represented by the reaction: CH4 (g) + 2 O2 (g) ⇋ CO2 (g) + 2 H2O (g) Figure out whether the enthalpy change for this process is substantially negative (ΔH < 0), substantially positive (ΔH > 0), or close to zero (ΔH ≈ 0). Next figure out whether the entropy change is substantially negative, substantially positive, or close to zero. Pick the correct choice from the multiple choices based on your reasoning. A. For this process, ∆H > 0 and ∆S > 0 B. For this process, ∆H ≈ 0 and ∆S < 0 C. For this process, ∆H < 0 and ∆S 0 and ∆S > 0 21. Which of the following statements is NOT a correct representation of the First Law of Thermodynamics? A. “You can’t get something for nothing.” B. Entropy of an isolated system always increases. C. Energy lost by the system must be gained by the surroundings. D. The total amount of matter and energy in the universe is constant. E. In any process, energy can be changed from one form to another, but can neither be created nor destroyed. 22. What is the molar solubility of BaSO4 in water at 25oC? Ksp of BaSO4 at this temperature is 1.10 × 10–10 A. 1.85 × 10-7 B. 5.50 × 10-11 C. 1.05 × 10-5 D. 2.85 × 10-3 E. 2.14 × 10-5 10 23. Consider the following reaction: 2 Cl2 (g) + 2 H2O (g) ⇋ 4 HCl (g) + O2 (g) The enthalpy change at 298 K for this reaction is ΔHorxn = 114.44 kJ/mol. The entropy change for this reaction under the same conditions is ΔSorxn = 128.18 J/mol- K. Calculate the value of ΔGrxn at a temperature of 700 K. Assume that ΔHorxn and ΔSorxn do not change with temperature. A. At this temperature, ΔGrxn = 24.7 kJ/mol B. At this temperature, ΔGrxn = 31.3 kJ/mol C. At this temperature, ΔGrxn = 153.1 kJ/mol D. At this temperature, ΔGrxn = 712.6 kJ/mol E. At this temperature, ΔGrxn = 140.6 kJ/mol 24. Consider the following reaction: P2 (g) + 3 Cl2 (g) ⇋ 2 PCl3 (g) For the reaction above, ∆Gorxn = –642.9 kJ/mol at 298 K. What is the ∆G for this reaction at 298 K given the partial pressure of 15.0 atm PCl3, 10.0 atm Cl2, and 2.00 atm PCl3. Use R = 8.314 J/K for the value of the gas constant A. ∆G = –256.3 kJ/mol B. ∆G = –576.4 kJ/mol C. ∆G = –663.3 kJ/mol D. ∆G = –801.9 kJ/mol E. ∆G = –117.8 kJ/mol 11 25. When 1.50 g of phenol, C6H5O6, is combusted in a bomb calorimeter, the temperature of the calorimeter increases from 23.54oC to 37.86oC. In a separate experiment, the heat capacity of the calorimeter is measured to be 11.66 kJ/oC. Calculate the heat of reaction, ΔHorxn (in kJ/mol) for the combustion of a mole of phenol in this calorimeter. Molar mass of phenol is 94.11 g/mol A. ΔHo = –1.05 x 104 kJ/mol B. ΔHo = 3.24 x 104 kJ/mol C. ΔHo = 2.07 x 103 kJ/mol D. ΔHo = 1.59 x 103 kJ/mol E. ΔHo = 6.91 x 105 kJ/mol 26. BONUS. Which of the following salts will be least soluble in water, i.e., give the lowest concentration of [Ag+]? A. AgCl Ksp = 1.8 x 10-10 B. AgBr Ksp = 5.0 x 10-13 C. AgI Ksp = 8.3 x 10-17 D. AgF Ksp = 1.8 x 10-8 E. AgBrO3 Ksp = 5.5 x 10-13 12 Scratch paper 13 Scratch paper 14