Question

Heat evolved in the reaction $H_2 + Cl_2 \to 2HCl$ is $182 kJ$. Bond energies of $H - H$ and $Cl - Cl$ are $430$ and $242 \,kJ/mol^{-1}$ respectively. The $H - Cl$ bond energy is

• A. $245\, kJ\, mol^{-1}$
• B. $427\, kJ\, mol^{-1}$
• C. $336\, kJ\, mol^{-1}$
• D. $154\, kJ\, mol^{-1}$

Answer 1

Answer: (A)

$\Delta H=-2\times\varepsilon_{H-Cl}+\varepsilon_{H-H}+\varepsilon_{Cl-C}$
$\therefore 182=-2\times a+430+242$
$\therefore a=245 kJ mol ^{-1}$