Question

The bond dissociation energy of $C-H$ in ${CH}_4$ from the equation
$C\left(g\right)+4H\left(g\right)\to {CH}_4\left(g\right);\Delta H=-397.8kcal$ is:

• A. $+99.45kcal$
• B. $-99.45kcal$
• C. $+397.8kcal$
• D. $+198.9kcal$

Answer 1

The correct option is A $+99.45kcal$

$\Delta H$ of the given reaction,
$C\left(g\right)+4H\left(g\right)\to C{H}_4\left(g\right)$
can be written as, $\Delta H={\text{heat released in formation of 4 C-H bonds in CH}}_4$
=> $\Delta H=-4\times {\text{bond dissociation energy of C-H bond in CH}}_4$
=> $-397.8=-4\times {\text{bond dissociation energy of C-H bond in CH}}_4$
=> ${\text{bond dissociation energy of C-H bond in CH}}_4=99.45Kcal$
Hence, answer is option A.