Question

The heat of combustion of ethane, ethylene and hydrogen are $372.79kcal$, $337.0kcal$ and $68.4kcal$ respectively. What is the heat evolved in the reaction?
$C_2{H}_4+H_2⟶C_2{H}_6$?

• A. $-32.61kcal$
• B. $+32kcal$
• C. $68.4kcal$
• D. None of these

Answer 1

Answer: (A)

$-32.61kcal$

$H_2+\frac{1}{2}{O}_2⟶H_{2}O+\mathrm{68.4........}\left(i\right)$
$C_2{H}_4+3O_2⟶2{CO}_2+2H_{2}O+\mathrm{3337.0......}\left(ii\right)$
$C_2{H}_6+\frac{7}{2}{O}_2⟶2{CO}_2+3H_{2}O+\mathrm{372.79.....}\left(iii\right)$
Onreversing eq $\left(iii\right)$ we get
$2{CO}_2+3H_{2}O+372.79⟶c_2{H}_6+\frac{7}{2}{O}_2.....\left(iv\right)$
On adding Eqs. $\left(i\right),\left(ii\right),\left(iv\right)$ we get
$C_2{H}_4+H_2+372.79=C_2{H}_6+68.4+337$
$C_2{H}_4+H_2⟶C_2{H}_6+32.61$
$\Delta H=-32.61kcal$