Chemical Thermodynamics Question 387

Question: The enthalpy of atomisation of $ CH_4 $ and $ C_2H_6 $ are 360 and $ 620kcalmo{{l}^{-1}} $ respectively. The $ C-C $ bond energy is expected to be

Options:

A) $ 210kcalmo{{l}^{-1}} $

B) $ ~80kcalmo{{l}^{-1}} $

C) $ 130kcalmo{{l}^{-1}} $

D) $ 180kcalmo{{l}^{-1}} $

Show Answer

Answer:

Correct Answer: B

Solution:

  • Atomisation of methane $ CH_4( g )\xrightarrow{{}}C( g )+4H( g ); $

$ \Delta H=360kcal $

$ \therefore C-H $ bond energy $ =\frac{360}{4} $

$ =90kcalmo{{l}^{-1}} $

$ C_2H_6(g)\xrightarrow{{}}2C(g)+6H(g); $

$ \Delta H=620kcal $ or $ {H_{C-C}}+6{H_{C-H}}=620 $

$ \therefore {H_{C-C}}=620-6{H_{C-H}} $

$ =620-6\times 90=80kcalmo{{l}^{-1}} $



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