Calculate the heat of formation of anhydrous `Al_2Cl_6` from the following data:
(i) `2Al + 6HCl (aq) to Al_2Cl_6 (aq) + 3H_2(g), DeltaH = - 239.76 kcal `
(ii) `Al_2Cl_6 (s) + aq to Al_2Cl_6(aq), DeltaH = - 153.69 kcal `
(iii) `H_2(g) + Cl_2(g) to 2HCl (g) , DeltaH = -44kcal`
(iv) `HCl (g) + aq to HCl (aq), DeltaH = - 17.31 kcal`

Explanation

To calculate the heat of formation of anhydrous \( \text{Al}_2\text{Cl}_6 \), we will use Hess's law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps of the reaction.

### Step-by-Step Solution:

1. **Identify the target reaction**:
The formation of anhydrous \( \text{Al}_2\text{Cl}_6 \) from its elements can be represented as:
\[
2 \text{Al} (s) + 3 \text{Cl}_2 (g) \rightarrow \text{Al}_2\text{Cl}_6 (s)
...