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Question: The bond dissociation energy of \(CH\) in \[C{H_4}\] ​from the equation \(C(g) + 4H(g) \to C{H_4}(...

The bond dissociation energy of CHCH in CH4C{H_4} ​from the equation
C(g)+4H(g)→CH4(g)C(g) + 4H(g) \to C{H_4}(g) , ΔH=−397.8kcal\Delta H = - 397.8kcal
A) +99.45kcal
B) -99.45kcal
C) +397.8kcal
D) +198.9kcal

Explanation

Solution

Carbon and Hydrogen are in their elementary states so their enthalpies will be zero (0). Bond dissociation energy measures the strength of bond. Or we can say that bond dissociation energy is the energy required to dissociate the bond.

Complete answer:
Given balanced equation is C(g)+4H(g)→CH4(g)C(g) + 4H(g) \to C{H_4}(g) , ΔH=−397.8kcal\Delta H = - 397.8kcal
Since Carbon and Hydrogen in this reaction are in their elementary state so their enthalpies will be “0”
And enthalpy for the reaction is ΔH=−397.8kcal\Delta H = - 397.8kcal
So as enthalpies of carbon and hydrogen are zero therefore enthalpy of CH4C{H_4}= 397.8kcal397.8kcal
And since there are 4CH4CH bonds in CH4C{H_4}
Therefore it can be written as, ΔH\Delta H = heat released in formation of 4CH4CH bonds in CH4C{H_4}
ΔH\Delta H=4×4 \times bond dissociation energy ofCHCH bond in CH4C{H_4}
397.8kcal397.8kcal = 4×4 \times bond dissociation energy of CHCH bond in ​CH4C{H_4}
Bond Dissociation energy of CHCH bond in ​CH4C{H_4}=397.8÷4397.8 \div 4.
Therefore, Bond Dissociation energy of CHCH bond in ​CH4C{H_4}= +99.45kcal+99.45kcal

Hence, the correct answer is option ‘A’.

Note: Bond dissociation energy is one which measures strength of bond. Elements or compounds which are in their elementary state have enthalpies zero as in this question enthalpies of carbon and hydrogen is zero because they are present in their elemental states.