Q9.77CP - Chemistry: Molecular Nature Of Matter And Change

Question

How much energy is released in the formation of one molecule of HCl by the following reaction? ${\mathbf{H}}^{+}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\mathbf{+}\mathbf{C}{\mathbf{l}}^{-}\mathbf{\left(}\mathbf{g}\mathbf{\right)}\to \mathbf{HCl}\mathbf{\left(}\mathbf{g}\mathbf{\right)}$  The bond energy of HCl is 431 kJ mol^-1. Additional data can be found in tables in Chapter 8?

Step-by-Step Solution

Answer

$\mathbf{7}\mathbf{.}\mathbf{15}\mathbf{*}{\mathbf{10}}^{-19}\mathbf{J}$  is the amount of energy released in the formation of one molecule of HCl.

Mole concept

Number of molecules in 1 mole of HCl =  $\mathbf{6}.\mathbf{022}*{\mathbf{10}}^{23}$

Energy released

The energy calculated above is for one mole of HCl 

For one molecule of HCl, the energy is divided by Avogadro’s number (6.022* ${10}^{23}$)

Therefore

The energy released per molecule of HCl formed is  $\mathbf{=}\frac{431000J}{\mathbf{6}\mathbf{.}\mathbf{022}\mathbf{*}{\mathbf{10}}^{23}}$

                                                                                         $\mathbf{=}\mathbf{7}\mathbf{.}\mathbf{15}\mathbf{*}{\mathbf{10}}^{-19}\mathbf{J}$