Answer :
Final answer:
The average C-H bond energy in CH4(g) is 415 kJ/mol because there are four moles of C-H bonds broken per mole of the reaction. Although the four C-H bonds are equivalent in the original molecule, they do not each require the same energy to break; once the first bond is broken (which requires 439 kJ/mol), the remaining bonds are easier to break. The 415 kJ/mol value is the average, not the exact value required to break any one bond.
Explanation:
The bond enthalpies in Table T3 allows us to calculate ΔH because 2 C=O and 2 C-O bonds are formed:
AH ≈ 2 mol (-192.0 kJ mol-¹) + 2 mol (-85.5) = -555 kJ
The average C-H bond energy, Dc-H, is 415 kJ/mol because there are four moles of C-H bonds broken per mole of the reaction. Although the four C-H bonds are equivalent in the original molecule, they do not each require the same energy to break; once the first bond is broken (which requires 439 kJ/mol), the remaining bonds are easier to break. The 415 kJ/mol value is the average, not the exact value required to break any one bond.
