Thermodynamics

Consider the following data.

(i) $2\text{Al(s)} + 6\text{HCl(aq)} \rightarrow \text{Al}_2\text{Cl}_6\text{(aq)} + 3\text{H}_2\text{(g)} + 1200~\text{kJ/mol}$

(ii) $\text{H}_2\text{(g)} + \text{Cl}_2\text{(g)} \rightarrow 2\text{HCl(g)} + 164~\text{kJ/mol}$

(iii) $\text{HCl(g)} + \text{aq} \rightarrow \text{HCl(aq)} + 83~\text{kJ/mol}$

(iv) $\text{Al}_2\text{Cl}_6\text{(s)} + \text{aq} \rightarrow \text{Al}_2\text{Cl}_6\text{(aq)} + 663~\text{kJ/mol}$

The enthalpy of formation of anhydrous solid $\text{Al}_2\text{Cl}_6$ is :