Question

Heat evolved in the reaction $H_2+{Cl}_2\to 2HCl$ is $182kJ$.

( Bond energies $H-H=430kJ/mole,Cl-Cl-242kJ/mole$). The $H-Cl$ bond energy is:

• A. $763kJ/mole$
• B. $427kJ/mole$
• C. $336kJ/mole$
• D. $154kJ/mole$

Answer 1

The correct option is B $427kJ/mole$

$\frac{1}{2}{H}_2+\frac{1}{2}C{l}_2⟶HCl$

${\Delta }_{f}H=\Delta H_{B{E}_{Reactants}}-\Delta H_{B{E}_{Products}}$

$-90$ = $\frac{1}{2}430+\frac{1}{2}242$ - BE of HCl

BE of $HCl=215+121+90=426\approx 427kJ/mole$

Hence the answer is $427kJ/mole$