Calculate the C-C bond energy in ethane from the following data.
ΔH_f (CH₄, g) = -75 kJ/mol
ΔH_f (C₂H₆, g) = -84 kJ/mol
Enthalpy of sublimation of C (graphite) = 717 kJ/mol
H-H bond energy = 436 kJ/mol
(Assume the C-H bond energy is the same in both hydrocarbons.)

Question

Calculate the C-C bond energy in ethane from the following data.

ΔH_f (CH₄, g) = -75 kJ/mol

ΔH_f (C₂H₆, g) = -84 kJ/mol

Enthalpy of sublimation of C (graphite) = 717 kJ/mol

H-H bond energy = 436 kJ/mol

(Assume the C-H bond energy is the same in both hydrocarbons.)

TestHub · Accepted Answer

Step 1, C-H from methane: CH 4 → C(g) + 4H(g). ΔH = 75 + 717 + 2(436) = 1664 kJ, so C-H = 416 kJ/mol. Step 2, atomise ethane: C 2 H 6 → 2C(g) + 6H(g). ΔH = 84 + 2(717) + 3(436) = 2826 kJ. Ethane has 6 C-H and 1 C-C: 6(416) + E C-C = 2826. E C-C = 2826 - 2496 = 330 kJ/mol. (Using the textbook 413 for C-H would give 348, a trap.) Answer: (B).

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