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TA practice exam 3 key


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Unformatted text preview: 2054 kJ mol 4. 2700 kJ mol 1 In order to do this calculation, we need to find how many bonds are broken and how many bonds are formed of each type. Sometimes it’s easiest to make a table (all values in kJ mol 1 ) Bonds broken Type Number Bond Energy Total Energy C‐C 2 347 700 C‐H 8 413 3200 O=O 5 498 2500 Total bonds broken energy 6500 kJ mol 1 Bonds formed Type Number Bond Energy Total Energy O‐H 8 464 3600 C=O 6 805 4800 Total bonds formed energy 8400 kJ mol 1 If we do bonds broken minus bonds formed, then the enthalpy of the reaction is 1900 kJ mol 1 which is very close to the value 2054 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 correct 3. 12 L atm 4. 8 L atm Since the all of answers are in units of L atm , we don’t have to worry about converting. The relevant equation is w pV In this case w 4 atm 3 L 1 L w 8 L atm 13. Which of the following could be used to calculate the change in internal energy of an ideal gas? I. Change in temperature and the identity of the gas II. Both the heat and the work of the process 1. I only 2. II only 3. I and II correct 4. None of the above 1 For an ideal gas, E Nk T , where N is the number of atoms in each molecule. Additionally, 2 E q w . Thus, both can be used. 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 correct 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 A calorimetry experiment relies on the fact that the energy of the universe is constant, which means that all heat produced by the reaction is transferred to the surroundings. 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...
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