Calculate the C–C bond enthalpy from the following data :

Chemistry Thermodynamics and Thermochemistry General Single Correct MCQ

Published by: CGP EDU Academic Team

Published on: August 13, 2026

C(s) ⎯→ C(g) ; Δ H = 170 Kcal

H 2 (g) ⎯→ H(g) ; Δ H = 52 Kcal

Heat of formation of ethane = – 20 Kcal

C–H bond enthalpy = 99 Kcal.

Text Solution

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(78 Kcal )

2C (g) + 3H 2 (g) ⎯→ C 2 H 6 (g) Δ H reaction = Δ H f º (C 2 H 6 ) .........(i)

2C (s) ⎯→ 2C (g) Δ H 1 = 2 × 170 Kcal .........(ii)

equations (i) + (ii)

2C (s) + 3H 2 (g) ⎯→ C 2 H 6 (g)

Δ H reaction = Δ H f º (C 2 H 6 ) = Δ H 1 + 3 Δ H H–H – 6 Δ H C–H – Δ H C–C

– 20 = 340 + 3 × 104 – 6 × 99 – Δ H C–C

Δ H C–C = 78 Kcal.

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