Question

The $H-H$ bond energy is $430 \,kJ$ mole $^{-1}$ and $Cl - Cl$ bond energy is $240 \,k J$ mole $^{-1}, \Delta H$ for $H C l$ is $-90 \, k J$. The $H-C l$ bond energy is about:

• A. $180 \,k J$ mole $^{-1}$
• B. $360\, k J$ mole $^{-1}$
• C. $213 \,k J$ mole $^{-1}$
• D. $425 \,k J$ mole $^{-1}$

Answer 1

Answer: (D)

$\frac{1}{2} H_{2}+\frac{1}{2} C l_{2} \rightarrow H C l ;$
$\Delta H=-90 \,k J$
$-\Delta H=\frac{1}{2} B \cdot E \cdot(H-H)+\frac{1}{2} B \cdot E(C l-C l)$
or $-90=\frac{1}{2}[430]+\frac{1}{2}[240]-B \cdot E \cdot(H-C l)$
or $-90=215+120-B \cdot E \cdot(H-C l)$
B. $E \cdot(H-C l)=215+120+90$
$=425\, k J$ mole $^{-1}$