TA practice exam 3 key

# Giventhefollowingdata h f kj mol 1 substance

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Unformatted text preview: t capacity of the calorimeter in kJ / C ? a. 51.98 kJ C correct b. 56.76 kJ C c. 25.99 kJ C d. 1200 kJ C H mcT Cb T where c is the heat capacity of water and Cb is the heat capacity of the bomb. Rearranging this expression to solve for Cb , H mcT Cb T Since approximately 1 mol of ethanol was used, H -1368 kJ . Thus, 2808 kJ 1000 g 4.18 J C 1 g 1 50 C Cb 50 C Cb 51.98 kJ C Without a calculator, round 2808 to 2800, 4.18 to 4 and solve this way 2800 kJ 1000 g 4 J C 1 g 1 50 C Cb 50 C 2600 kJ Cb 50 C Cb 52 kJ C 8. Given the following data H f kJ mol 1 Substance 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 correct 1 4. 0 kJ mol 5. 718.71 kJ mol 1 We are looking for the reaction H 2SO 4 l 2H + aq SO2 (aq) 4 The enthalpy of this reaction is H rxn H f SO 2 (aq ) 2 H f H + aq H f H 2 SO 4 l 4 which is H rxn 909.27 kJ mol 1 813.99 kJ mol 1 H rxn 95.28 kJ mol 1 9. Given the following set of reactions P4 (s) + 6Cl2 (g) 4PCl3 (g) H 2439 kJ 4PCl5 (g) P4 (s) + 10Cl2 (g) H 3438 kJ What is the enthalpy of reaction of PCl5 (g) PCl3 (g) + Cl2 (g) ? 1. 4000 kJ 2. 1000 kJ 3. 250 kJ correct 4. 250 kJ 5. 1000 kJ 6. 4000 kJ The best way to get this reaction is to add reaction 1 and reaction 2, and then divide everything by 4. Thus, 2439 kJ 3438 kJ H 4 H 250 kJ 10. Assuming all vibrational modes are active, which of the following ideal gases has the highest internal energy? 1. 1 mol of helium at 300 K 2. 1 mol of nitrogen at 300 K 3. 1 mol of argon at 300 K 4. 1 mol of carbon dioxide at 300 K 5. 1 mol of carbon dioxide at 1000 K correct when all vibrational modes are active, the internal energy of 1 mol of an ideal gas is 1 E N RT 2 where N is the number of atoms in the molecule. Upon inspection, we can see that He = Ar < N2 < CO2 at 300 K, because carbon dioxide has more atoms than the other 3 species. 1 When we then apply the formula E N RT to the two carbon dioxide cases, it becomes clear 2 that carbon dioxide at 1000 K has the highest internal energy. 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 correct 1 3....
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