1.The enthalpy change for the following reaction is -802 kJ. Using bond energies, estimate the C-H bond energy in CH4(g).

CH4(g) + 2O2(g)CO2(g) + 2H2O(g)

answer needs to be in kJ/mol

2.The enthalpy change for the following reaction is -137 kJ. Using bond energies, estimate the C-C bond energy in C2H6(g).

C2H4(g) + H2(g)C2H6(g)


kJ/mol

3.The enthalpy change for the following reaction is 10.4 kJ. Using bond energies, estimate the I-I bond energy in I2(g).

H2(g) + I2(g)2HI(g)


kJ/mol

I am helping you in first question
1.The enthalpy change for the following reaction is -802 kJ. Using bond energies, estimate the C-H bond energy in CH4(g).

CH4(g) + 2O2(g)---->CO2(g) + 2H2O(g)

These questions are based on the concept that all bonds are broken for the reactants (energy is required )and  bonds are formed in the products (energy is released).
Now you need to add bond enthalpies required for reactants and add bond enthalpies of the products and take the difference to get the detla H of the reaction.

Delta H = sum of BE (Reactants)-sum of BE(products)




1.The enthalpy change for the following reaction is -802 kJ. Using bond energies, estimate the C-H bond energy in CH4(g).

CH4(g) + 2O2(g)----CO2(g) + 2H2O(g)
Reactants                                                                                                                                                               
                                                                                                                                                                                                                                                                       
4C-H bonds = 4x(assumed as x)                                                                   
   
2O==O = 2(check from the bond enthalpy table for O=O)               
Sum all BE     (reactants)   
Products
2 C=O          =2( from table for C=O  )   

       4H-O   = 4(from BE table H-O)                                                                                                                                         

                                                                                                                                   

Sum all BE(products)                                                                             


Delta H = sum of BE (Reactants)-sum of BE(products)
Try rest of the questions exactly in this way

Thank You so much your explanation helped me to solve these problems.