Anhydrous cobalt(II) chloride, CoCl2\text{CoCl}_2CoCl2, is a blue solid that hydrates in the presence of water to form a pink hexahydrate, CoCl2⋅6H2O\text{CoCl}_2\cdot 6\text{H}_2\text{O}CoCl2⋅6H2O.
CoCl2(s)+6H2O(l)→CoCl2⋅6H2O(s)\text{CoCl}_2(\text{s}) + 6\text{H}_2\text{O}(\text{l}) \rightarrow \text{CoCl}_2\cdot 6\text{H}_2\text{O}(\text{s})CoCl2(s)+6H2O(l)→CoCl2⋅6H2O(s)
Explain why it is not possible to measure the enthalpy change for this reaction directly using a simple cup calorimeter.
The enthalpies of solution for the anhydrous and hydrated cobalt(II) chloride salts are given in the table below:
| Substance | Enthalpy of solution / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| CoCl2(s)\text{CoCl}_2(\text{s})CoCl2(s) | −82.4-82.4−82.4 |
| CoCl2⋅6H2O(s)\text{CoCl}_2\cdot 6\text{H}_2\text{O}(\text{s})CoCl2⋅6H2O(s) | +3.8+3.8+3.8 |
By constructing an appropriate Hess's Law cycle, calculate the standard enthalpy change for the hydration of anhydrous cobalt(II) chloride to form the hexahydrate salt.