Question

Problem 5.83

Use bond enthalpies in the table below to estimate ?H for each of the following reactions.

Problem 5.83 Part A Use bond enthalpies in the table below to estimate ? 1 for each of the following reactions H-H(g) + Br-Br(g) ? 2H-Br(g) Express your answer in kilojoules to 3 significant figures Average Bond Enthalpies (kJ/mol) 103 kJ 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 CI-F 253 C-N 293 N-F 272 O-F 190 CI-Cl 242 C-O 358 N-C 200 O-Cl 203 |Br-F 237 C=O 799 N-Br 2430-1 234 Br-C1218 C-F 485 H-H 436 C-Cl 328 H-F 567 C-Br 276 H-C 431 C-I 240 H-Br 366 Submit My Answers Give Up Correct Part B Br-Br 193 I-Cl 208 I-Br 175 I-I 151 H-I 299 Express your answer in kilojoules to 3 significant figures 303 kJ Submit My Answers Give Up Incorrect; Try Again; 9 attempts remaining

Answer 1

The reaction is 2CH3-0-H-30-O-> 20-C-0+4H-O-H The bond enthalpy values for C-H, C-O, O-Н, О-O, and C 463 k/mol, 495 kJmol, and 799 kJ/mol respectively. O are 413 kJ/mol, 358 kJ/mol The enthalpy change for the above reaction is calculated as follows: AHAB product 2 mol 2(B.E +4mol 2(BE = 2 moi [3(413 kJ/mol)]+2 mol [1(358 kJ/mol)]+2 mol [1463 kJ/mol)] +3 mol [1(49 mo2(799 kJmol)1+4mol [2(463 kJmol kJ/mol) -2 --1.29x 10 kJ Hence, the enthalpy change is 1.29x10

Answer 2

Part A The value for AHis calculated by the formula as shown below: AHmn = Σ (AH for bonds broken)-(AH for bond formation) The reaction is shown below, and calculate the AHas shown below: H-H(g)+Br-Br(g)2H-Br(g) AH for bonds broken (H-H) 436 kJ/mol 193 kJ/mol r-Br ΔΗ 436 +193 = 629 kJ/mol AFI for bonds formed : 2(H-Br) 2(366) 732 kJ/mol ΔΗ 732 kJ/mol The ΔΗ, ,is calculated as shown below: AH 629kJ/mol-732kJ/mol --103 kJ/mol Therefore, AH is 103kJ/mol

Part B The value for AHis calculated by the formula as shown below: AHAH for bonds broken)-(AH for bond formation) The reaction is shown below, and calculate the AHas shown below: 2H AH for bonds broken : 2(3(C-H)) 6(413) 2(C-O)2(358) 2(O-H) 2(463) 3(O-O) 3(495) 2478 kJ/mol 716 kJ/mol 926 kJ/mol 1485 kJ/mol AH 2478 716926+1485 - 5605 kJ/mol AH for bonds formed 2{2(C-O)) 4(799) 412(o-H) 8(463) 3196 kJ/mol 3704 kJ/mol AH 3196+ 3704 - 6900 kJ/mol The AHan 1s calculated as shown below: AH 5605kJ/mol -6900kl/mol --1295 kJ/mol Therefore, AHis 1295 kJ/mol