TA practice exam 3 - CH301 Fall 2010 Practice Exam 3 1....

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Unformatted text preview: CH301 Fall 2010 Practice Exam 3 1. Which of the following statements is/are true? I. If a gas both expands and releases heat, then the internal energy of the gas must decrease. II. If a gas both expands and absorbs heat, then the internal energy of the gas must decrease. III. If a gas both contracts and absorbs heat, then the internal energy of the gas must increase. 1. I only 2. II only 3. III only 4. I and II only 5. II and III only 6. I and III only 7. I, II, and III 8. None of the above 2. Why can a bomb calorimeter be used to estimate the enthalpy of a combustion reaction, even though the reaction is conducted at constant volume? 1. The pressure change in the system can be measured 2. The temperature change in the system can be measured 3. The contribution from the change in the volume is very small compared to the change in the energy associated with the reaction. 4. You can’t use a bomb calorimeter to estimate the enthalpy of a combustion reaction 3. An ideal gas is compressed adiabatically (no heat is absorbed or released). What are the signs of E , q, and w? E q w 1. + + + 2. + ‐ ‐ 3. 0 + ‐ 4. 0 0 0 5. + 0 + 6. ‐ 0 ‐ 4. Which of the following is NOT a state function? 1. E 2. H 3. S 4. q 5. G 5. Which of the following would have a zero enthalpy of formation at 298 K? 1. H 2O(l) 2. H 2O(g) 3. Cgraphite 4. Cdiamond 5. none of the above 6. Given the following table of heat capacities: Iron: 25 J mol 1K 1 Nickel: 26.07 J mol 1K 1 Copper: 24.440 J mol 1K 1 Rhodium: 24.98 J mol 1K 1 Imagine I take 1 mol of each of these substances at 1000 K and throw each of them into an Olympic size swimming pool. Which pool will have the highest temperature after the pool‐metal system has come to equilibrium? Ignore the effects of the air surrounding the pool cooling the system. 1. Pool + iron 2. Pool + nickel 3. Pool + copper 4. Pool + rodium 7. When burned, glucose has a Erxn of 2808 kJ mol 1 . Suppose that 1 mol of pure glucose was burned in a bomb calorimeter containing 1 L of water. If the temperature increases by 50 C after the reaction occurs, what is the heat capacity of the calorimeter in kJ / C ? a. 51.98 kJ C b. 56.76 kJ C c. 25.99 kJ C d. 1200 kJ C 8. Given the following data H f kJ mol 1 Substance H 2SO4 l ‐813.99 SO2 (aq) ‐909.27 4 + H aq 0 Calculate the enthalpy of the reaction of sulfuric acid completely dissociating in water into H + and SO2 298 K. 4 1. 718.71 kJ mol 1 2. 95.28 kJ mol 1 3. 95.28 kJ mol 1 1 4. 0 kJ mol 5. 718.71 kJ mol 1 9. Given the following set of reactions H 2439 kJ P4 (s) + 6Cl2 (g) 4PCl3 (g) H 3438 kJ 4PCl5 (g) P4 (s) + 10Cl2 (g) What is the enthalpy of reaction of PCl5 (g) PCl3 (g) + Cl2 (g) ? 1. 4000 kJ 2. 1000 kJ 3. 250 kJ 4. 250 kJ correct 5. 1000 kJ 6. 4000 kJ 10. Assuming all vibrational modes are active, which of the following ideal gases has the highest internal energy? 1. 2. 3. 4. 5. 1 mol of helium at 300 K 1 mol of nitrogen at 300 K 1 mol of argon at 300 K 1 mol of carbon dioxide at 300 K 1 mol of carbon dioxide at 1000 K 11. Given the following data on bond energies. Bond Type Bond Energy kJ mol 1 C‐C 347 O‐H 464 C‐H 413 O=O 498 C=O 805 Calculate the reaction enthalpy of C 3H 8 ( g ) 5O 2 3CO 2 ( g ) 4H 2O (l ) 1. 2700 kJ mol 1 2. 2054 kJ mol 1 1 3. 2054 kJ mol 4. 2700 kJ mol 1 12. A gas expands from 1 L to 3 L against a constant pressure of 4 atm. What is the value of w for this process? 1. 12 L atm 2. 8 L atm 3. 12 L atm 4. 8 L atm 13. Which of the following could be used to calculate the change in internal energy of an ideal gas? I. II. 1. 2. 3. 4. Change in temperature and the identity of the gas Both the heat and the work of the process I only II only I and II None of the above 14. Calorimetry experiment calculations rely on which of the three laws of thermodynamics? I. The first law II. The second law III. The third law 1. I only 2. II only 3. III only 4. I and II only 5. II and III only 6. I and III only 7. I, II, and III 8. None of the above 15. A runner works off 16000 kJ of energy while running. During the run, he did 12000 kJ of work on the surroundings. What is the magnitude of the heat released by the runner during his run? 1. 2. 3. 4. 38000 kJ 12000 kJ 4000 kJ 16000 kJ 16. Which of the following reactions would have a positive entropy change? I. H 2O(g) H 2O l II. CO 2 ( s ) CO 2 ( g ) III. C 3H 8 ( g ) 5O 2 3CO 2 ( g ) 4H 2O (l ) 1. I only 2. II only 3. III only 4. I and II only 5. II and III only 6. I and III only 7. I, II, and III 8. None of the above 17. Calculation entropy change at a phase transition Which of the following transitions would have the largest value for Ssystem ? 1. H 2O(g) H 2O l 2. H 2O(l ) H 2O g 3. H 2O(s ) H 2O l 4. H 2O(l ) H 2O s 18. When deciding whether or not a process is spontaneous, one only needs to look at the sign of _____________. 1. Ssystem 2. H 3. Suniverse 4. Ssurroundings 19. Which of the following is a consequence of the third law of thermodynamics? 1. The energy of the universe is constant 2. The entropy of the universe increases for any spontaneous process. 3. The entropy of any system is 0 at 0 K. 4. The entropy of a perfect crystal with only one possible orientation is 0 at 0 K. 5. Both 3 and 4 are correct. 20. If a molecule has two possible orientations how does the polarity of the molecule affect the entropy at 0 K? 1. The entropy is unaffected by polarity 2. The entropy of the system increases with increasing polarity 3. The entropy of the system decreases with increasing polarity 21. Which of the following compounds would have the highest standard molar entropy at 298 K? 1. CO 2 ( s ) 2. H 2O(l ) 3. Al ( s ) 4. H 2O g 22. Approximate the molar entropy of HCl at 0 K. Assume it has two possible orientations. 1. 5.76 J K 1 2. 0 J K 1 3. 8.31 J K 1 4. 5.76 J K 1 23. Given the following reaction G 142 kJ 2SO 2 ( g ) O 2 ( g ) 2SO 3 ( g ) What can be said with certainty if 2 mol of SO 2 ( g ) is mixed with 1 mol of O 2 ( g ) at room temperature? I. A significant amount of SO 3 ( g ) will be produced eventually II. A significant amount of SO 3 ( g ) will be produced rapidly III. Very little SO 3 ( g ) will be produced on the long time scale 1. I only 2. II only 3. III only 4. I and II only 5. II and III only 6. I and III only 7. I,II, and III 8. None of the above 24. The collective exhale from Auburn, Alabama at the end of the college football game released 3.0 10 8 J of heat into the surroundings. What is the increase in the entropy of the surroundings due to this exhale? Assume that the temperature was around 300 K. 1. 1 10 6 J K 1 2. 1 10 6 J K 1 3. 1 10 6 J K 1 6 1 4. 1 10 J K 5. 1 10 9 J K 1 6. 1 10 9 J K 1 25. Given the following information H f kJ mol 1 Substance HCN ( g ) 135.1 HCN (l ) 108.87 Estimate the boiling point of HCN at 1 atm. 1. 313 K 2. 100 K 3. 473 K 4. 253 K 5. 573 K J mol 201.78 112.84 1 K 1 26. Calculation involving the second law A process that has an entropy change of the system of 37 J K 1 also absorbs 30 kJ from the surroundings at 300 K. What is Suniverse for this process? 1. 137 J K 1 2. 63 J K 1 1 3. 63 J K 4. 137 J K 1 27. A reaction occurs spontaneously at 298 K. Which of the following statements could not possibly be true for this system? 1. Both S and H are positive 2. Both S and H are negative 3. S must be positive and H must be negative 4. S must be negative and H must be positive 28. A reaction does not occur spontaneously at 100 K but does occur at 1000 K. What are the signs of S and H for this reaction? S + + ‐ ‐ H + ‐ + ‐ 1. 2. 3. 4. 29. Problem predicting compound stability from delta G reaction Given the following reaction, OH + CH 3 CH 3OH (g) G 4000 kJ mol 1 What can you say about the relative stability of the products vs. the reactants. 1. 2. 3. 4. 5. The products are much more stable than the reactants. The reactants are much more stable than the products. The products are slightly more stable than the reactants The reactants are slightly more stable than the products. No information about stability can be concluded. 30. Given the following information H f kJ mol 1 Substance Sm J mol 1 K 1 H2 0 130.68 N2 0 191.61 NH 3 ‐46.11 192.45 Calculate the free energy change for the following reaction at 300 K. 3H 2 ( g ) N 2 ( g ) 2NH 3 ( g ) 1. 14 kJ mol 1 2. 32 kJ mol 1 1 3. 32 kJ mol 4. 14 kJ mol 1 ...
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