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}} $
