Question

given that bond energy of H-H and Cl-Cl are 430. kj/mol and 240 kj/mol respectively and ∆fH of HCl is -90 kj/mol. bond energy of HCl is
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Answer 1

Answer:

See below.

Explanation:

The formation of HCl is given by,

$H_{2}+Cl_{2}\rightarrow 2HCl$

The enthalpy of formation of 2 moles of HCl,

$\begin{aligned}\Delta _{f}H=-90 \ kJ \ mol^{-1}\\ 2\times \Delta _{f}H=-180 \ kJ \ mol^{-1}\end{aligned}$

To form two moles of HCl, we first need to break the H-H bond with the Cl-Cl bond. Then the two H+ and Cl- ions could form two HCl molecules.

Using Hess's Law,

$\begin{aligned}\Delta _{bond}H\left( HCl\right) =\left( -180\right) -\left( 430+240\right) \\ =-850 \ kJ \ mol^{-1} \end{aligned}$