Question

Heat evolved in the reaction ,$H_2\left(g\right)+C{l}_2\left(g\right)\to 2HCl\left(g\right)$ is $182kJ$. Bond energies $H-H=430kJ/mole$, and $Cl-Cl=242kJ/mole$. The $H-Cl$ bond energy is

• A. $763kJ/mole$
• B. $245kJ/mole$
• C. $336kJ/mole$
• D. $154kJ/mole$

Answer 1

The correct option is B $245kJ/mole$

$H_2+{Cl}_2⟶2HCl$

According to Hess's law,

$△H=(-182KJ)=B.E.(H-H)+B.E.(Cl-Cl)-2B.E.(H-Cl)$

$-182KJ=430+242-2\times B.E.(H-Cl)$

$B.E.\left(HCl\right)=\frac{854}{2}=427KJ/mol$.