Anhydrous magnesium sulfate, MgSO4\text{MgSO}_4MgSO4, can absorb water to form the hydrated salt magnesium sulfate heptahydrate, MgSO4⋅7H2O\text{MgSO}_4\cdot 7\text{H}_2\text{O}MgSO4⋅7H2O.
MgSO4(s)+7H2O(l)→MgSO4⋅7H2O(s)\text{MgSO}_4(\text{s}) + 7\text{H}_2\text{O}(\text{l}) \rightarrow \text{MgSO}_4\cdot 7\text{H}_2\text{O}(\text{s})MgSO4(s)+7H2O(l)→MgSO4⋅7H2O(s)
a.[1]
Suggest one reason why the enthalpy change for this reaction cannot be determined directly by calorimetry.
b.
[3]
Some enthalpies of solution are shown in the table below:
| Salt | Enthalpy of solution / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| MgSO4(s)\text{MgSO}_4(\text{s})MgSO4(s) | −91.2-91.2−91.2 |
| MgSO4⋅7H2O(s)\text{MgSO}_4\cdot 7\text{H}_2\text{O}(\text{s})MgSO4⋅7H2O(s) | +15.9+15.9+15.9 |
Calculate the enthalpy change for the hydration of anhydrous magnesium sulfate to form magnesium sulfate heptahydrate.