Q10.74CP - Chemistry: Molecular Nature Of Matter And Change

Question

In the 1980s, there was an international agreement to destroy all stockpiles of mustard gas, ${\mathbf{ClCH}}_2{\mathbf{CH}}_2{\mathbf{SCH}}_2{\mathbf{CH}}_2\mathbf{Cl}$ . When this substance contacts the moisture in eyes, nasal passages, and skin, the -OH groups of water replace the Cl atoms and create high local concentrations of hydrochloric acid, which cause severe blistering and tissue destruction. Write a balanced equation for this reaction, and calculate  $\mathbf{\Delta H}{\mathbf{°}}_{\mathrm{rxn}}$

Step-by-Step Solution

Answer

The heat of reaction is -217kJ

Step 1: Definition

The amount of heat that must be added or removed during a chemical reaction in order to keep all of the substances present at the same temperature is called the heat of reaction.

Step 2: Reaction

Mustard gas reacted with two molecules of water and replaces chlorine molecule 

and forms two molecules of hydrochloric acid.

 

Step 3: Heat of reaction

The bond energy of the C-Cl bond  $\mathbf{=}\mathbf{339}\mathbf{kJ}\mathbf{/}\mathbf{mol}$

The bond energy of the O-H bond  $\mathbf{=}\mathbf{467}\mathbf{kJ}\mathbf{/}\mathbf{mol}$

The bond energy of the C-O bond  $\mathbf{=}\mathbf{358}\mathbf{kJ}\mathbf{/}\mathbf{mol}$

The bond energy of the H-Cl bond  $\mathbf{=}\mathbf{427}\mathbf{kJ}\mathbf{/}\mathbf{mol}$

 

The energy required when bonds broken   $\mathbf{=}\mathbf{2}\mathbf{(}\mathbf{C}\mathbf{-}\mathbf{Cl}\mathbf{)}\mathbf{+}\mathbf{4}\mathbf{(}\mathbf{O}\mathbf{-}\mathbf{H}\mathbf{)}\mathbf{bonds}$

                                                                       $$\begin{gathered} \mathbf{=}\mathbf{1}\mathbf{\left(}\mathbf{339}\mathbf{\right)}\mathbf{+}\mathbf{4}\mathbf{\left(}\mathbf{467}\mathbf{\right)}\mathbf{kJ}\mathbf{/}\mathbf{mol} \\ \mathbf{=}\mathbf{2207}\mathbf{kJ}\mathbf{/}\mathbf{mol} \end{gathered}$$

      

The energy released when bonds formed  $\mathbf{=}\mathbf{2}\mathbf{(}\mathbf{C}\mathbf{-}\mathbf{O}\mathbf{)}\mathbf{+}\mathbf{4}\mathbf{(}\mathbf{H}\mathbf{-}\mathbf{Cl}\mathbf{)}\mathbf{Bonds}$

                                                                        $$\begin{gathered} \mathbf{=}\mathbf{2}\mathbf{\left(}\mathbf{358}\mathbf{\right)}\mathbf{+}\mathbf{4}\mathbf{\left(}\mathbf{427}\mathbf{\right)}\mathbf{kJ} \\ \mathbf{=}\mathbf{2424}\mathbf{kJ} \end{gathered}$$

       

Therefore, heat of reaction is  $\mathbf{=}(\mathbf{2207}\mathbf{-}\mathbf{2424})\mathbf{kJ}\mathbf{/}\mathbf{mol}\mathbf{=}\mathbf{-}\mathbf{217}\mathbf{kJ}$