Question

What is the heat of hydrogenation of ethene if the bond energies of $C-C$ , $C=C$ , $H-H$ , and $C-H$ are $350,600,440$ and $410kJ/mole$ respectively?

• A. $-130kJmol^{- 1}$
• B. $-260kJmol^{- 1}$
• C. $-400kJmol^{- 1}$
• D. $-450kJmol^{- 1}$

Answer 1

Answer: (A)

$\Delta H=\Sigma $ Bond energy of reactants
$-\Sigma $ Bond energy of products
$\Delta H=\left[4 \Delta H_{C - H} + \Delta H_{C = C} + \Delta H_{H - H}\right]$ $-\left[\Delta H_{C - C} + 6 \Delta H_{C - H}\right]$
$=\left[\right.4\times 410+600+440\left]\right.-\left[\right.350+2460\left]\right.$
$=2680-2810=-130kJmol^{- 1}$