Question

$H_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)⟶H_{2}O\left(g\right)$ $\Delta H=-242kJmo{l}^{-1}$

Bond energy of $H_2$ and $O_2$ are $436$ and $500$ $kJ$ mol${}^{-1}$ respectively. The bond energy of O$-$H bond is :

• A. $434$ $kJ$ mol${}^{-1}$
• B. $464$ $kJ$ mol${}^{-1}$
• C. $452$ $kJ$ mol${}^{-1}$
• D. $485$ $kJ$ mol${}^{-1}$

Answer 1

The correct option is B $464$ $kJ$ mol${}^{-1}$

$H_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)⟶H_{2}O\left(g\right);$ $\Delta H=-242kJmo{l}^{-1}$

$\Delta H=\text{Bond energy of reactants}-\text{Bond energy of products}$

$\Delta H=B_{H-H}+\frac{1}{2}{B}_{O-O}-2B_{O-H}$ ;

$-242kJ=436+\frac{1}{2}\left(500\right)-2B_{O-H}$

$-928kJ=-2B_{O-H}$

$\Rightarrow B_{O-H}=\frac{928}{2}$

$=464kJmo{l}^{-1}$

Hence, the bond energy of O-H bond is 464 kJ/mol.