bond dissociation enthalpy of CH4 is 360kJ/mol and C2H6 is 620kJ/mol. then bond dissociation energy of C-C bond is how much?

1. Bond dissociation enthalpy of CH‚Äč4 is the energy required to break four C-H bonds in it. 
   Thus, bond dissociation enthalpy for 1 C-H bond = Bond dissociation enthalpy for CH44 = 3604= 90 kJ/mol.

2. In C2H6 , thre are 6 C-H bonds and one C-C bond and the energy required to break all these bonds is 620 kJ/mol.

3. Thus, 

   Bond dissociation energy for C-C bond = Bond dissociation energy for C2H6 - 6 (Bond dissociation energy for one C-H bond)
                                                                 = 620 - 6 (90) = 620 - 540 = 80 kJ/mol.

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