Question

Use the bond energies provided to estimate AH'rxn for the reaction below. H :C=o: + 2H-H - → H-C-0-H - I O-119 kJ +137 kJ -555 bed -252 kJ +2731

Answer 1

Bond enthalpy or bond energy: The amount of energy required to break a bond between two atoms. Its unit is KJ/mol.

Bond enthalpy of the reaction = sum of the bond enthalpy in bonds broken(in reactants) - sum of the bond enthalpy in bond formed(in products)

Generally, the average bond enthalpy (in KJ/mol) is,

C triple bond O = 1072

H-H = 436

C-O = 358

C-H = 413

O-H = 463

for Bond Enthalpy of the reaction = [CO + 2(HH)] - [3(CH) + CO + OH]

= [1072 + 2(436)] - [3(413) + 358 + 463]

= 1944 - 2060

= -116 KJ

so from the options given, the closer one is the first option with -119KJ. The derived answer is different from the given option because the answer depends upon the values taken. So it won't be a problem.