Problem: Use bond enthalpies in the table below to estimate ΔH for each of the following reactions.Average Bond Enthalpies (kJ/mol)C-H 413N-H 391O-H 463F-F 155C-C 348N-N 163O-O 146C=C 614N-O 201O=O 495Cl-F 253C-N 293N-F 272O-F 190Cl-Cl 242C-O 358N-Cl 200O-Cl 203Br-F 237C=O 799N-Br 243O-I 234Br-Cl 218C-F 485H-H 436Br-Br 193C-Cl 328H-F 567C-Br 276H-Cl 431I-Cl 208C-I 240H-Br 366I-Br 175H-I 299I-I 151

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We have to calculate the enthalpy of reaction (ΔH) using the given bond enthalpies.


The change of enthalpy for a chemical reaction (ΔH) can be calculated using bond energies:

H = ΣBEreactants - ΣBEproducts

To determine the enthalpy of reaction, we need to first see what bonds are present in the reactants and the products.

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Problem Details

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

Average Bond Enthalpies (kJ/mol)

C-H 413N-H 391O-H 463F-F 155
C-C 348N-N 163O-O 146
C=C 614N-O 201O=O 495Cl-F 253
C-N 293N-F 272O-F 190Cl-Cl 242
C-O 358N-Cl 200O-Cl 203Br-F 237
C=O 799N-Br 243O-I 234Br-Cl 218
C-F 485H-H 436
Br-Br 193
C-Cl 328H-F 567

C-Br 276H-Cl 431
I-Cl 208
C-I 240H-Br 366
I-Br 175

H-I 299
I-I 151

The figure shows a reaction where 2 molecules of HCOH, with two H atoms bonded to the carbon (all bonds are single), react with 3 molecules consisting of two double-bonded O atoms. The products are two OCO molecules (all bonds are double) and 4 HOH molecules (all bonds are single).

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