Question

Consider the reactions
$C\left(s\right)+2H_2\left(g\right)⟶C{H}_4\left(g\right),\Delta H=-xkcal$
$C\left(g\right)+4H\left(g\right)⟶C{H}_4\left(g\right),\Delta H=-x_{1}kcal$
$C{H}_4\left(g\right)⟶C{H}_3\left(g\right)+H\left(g\right),\Delta H=+ykcal$
The average bond energy of $C-H$ bond in methane is

• A. $\frac{x}{4}kcalmo{l}^{-1}$
• B. $x_{1}kcalmo{l}^{-1}$
• C. $\frac{x_1}{4}kcalmo{l}^{-1}$
• D. $ykcalmo{l}^{-1}$

Answer 1

The correct option is C $\frac{x_1}{4}kcalmo{l}^{-1}$

$C\left(g\right)+4H\left(g\right)⟶C{H}_4\left(g\right);\Delta H=-x_{1}kcal$

Its reverse will be the reaction for the dissociation of methane which will give the dissociation energy of methane.
Average bond energy of C−H bond is = $\frac{\text{Dissociation energy of}C{H}_4}{\text{No. of bond broken}}=\frac{x_1}{4}$​​

Thus, the average bond energy of C−H bond in methane is = $\frac{x_1}{4}kcalmo{l}^{-1}$