Question

Energy required to dissociate $4g$ of gaseous hydrogen into free gaseous atoms is $208Kcal$ at ${25}^{o}C$. The bond energy of $H-H$ bond will be:

• A. $1.04Kcal$
• B. $10.4Kcal$`
• C. $104Kcal$
• D. $1040Kcal$

Answer 1

The correct option is C $104Kcal$

The reaction involved is,
$H_2\left(g\right)\to 2H\left(g\right)$

$\Delta H=\text{H-H bond energy}$

Since, $\text{moles =}\frac{\text{mass of compound}}{\text{molecular mass of compound}}$

So, $\text{moles of}{H}_2=\frac{4}{2}=2$

Hence, energy required to break 4gm or 2 moles of $H_2$ into gaseous atoms = $208Kcal=2\times \text{H-H bond energy}$

$\text{H-H bond energy}$ = $104Kcal$

Hence, answer is option C.