Sample Exercise 5.13 Part A Use the average bond enthalpies in the table to esti

Question

Sample Exercise 5.13 Part A Use the average bond enthalpies in the table to estimate H for the combustion of ethanol Average Bond Enthalpies (kJ/mol) C-H 413 N-H 391 O-H 463 F-F 155 C-C 348 N-N 163 O-O 146 C-C 614 N-O 201 O O 495 Cl-F 253 C-N 293 N-F 272 O-F 190 CI-CI 242 C-O 358 N-C 200 O-C 203 Br-F 237 C=O 799N-Br 2430-I 234 Br-Cl 218 C-F 485 H-H 436 C-CI 328 H-F 567 C-Br 276H-Cl 431 C-I 240 H-Br 366 Express your answer in kilojoules per mole to four significant figures Br-Br 193 kJ/mol I-Cl 208 I-Br 175 I-I 151 Submit My Answers Give Up H-I 299 Incorrect, Try Again; 3 attempts remaining

Explanation / Answer

The combustion reaction is

C2H5OH (l) + 7/2O2(g) --------------> 2CO2(g) + 3H2O(l)

Thus interms of bond energies

heat of reaction(combustion) = sum of bond energies of reactants - sum of bond energies of products

= [5xC-H +1xC-O +1xO-H +7/2xO=O] - [4xC=O + 6xO-H]

= [5x413 + 1x358 +1x463 + 7/2(495) ] - [4x799 + 6 x 463]

= -1355.5 kJ/mol

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