The standard enthalpy change of reaction, ΔrHθ\Delta_{\text{r}} H^{\theta}ΔrHθ, and the standard free energy change, ΔrGθ\Delta_{\text{r}} G^{\theta}ΔrGθ, for the hydration of anhydrous magnesium sulfate to magnesium sulfate heptahydrate at 298 K are shown below:
MgSO4(s)+7H2O(l)→MgSO4⋅7H2O(s) \text{MgSO}_4\text{(s)} + 7\text{H}_2\text{O(l)} \rightarrow \text{MgSO}_4\cdot7\text{H}_2\text{O(s)} MgSO4(s)+7H2O(l)→MgSO4⋅7H2O(s) ΔrHθ=−104.0 kJ mol−1 \Delta_{\text{r}} H^{\theta} = -104.0 \text{ kJ mol}^{-1} ΔrHθ=−104.0 kJ mol−1 ΔrGθ=−25.5 kJ mol−1 \Delta_{\text{r}} G^{\theta} = -25.5 \text{ kJ mol}^{-1} ΔrGθ=−25.5 kJ mol−1Standard entropies of the other species involved are given in the table below:
| Compound | Sθ / J K−1 mol−1S^{\theta}\text{ / J K}^{-1}\text{ mol}^{-1}Sθ / J K−1 mol−1 |
|---|---|
| MgSO4⋅7H2O(s)\text{MgSO}_4\cdot7\text{H}_2\text{O(s)}MgSO4⋅7H2O(s) | 372.0372.0372.0 |
| H2O(l)\text{H}_2\text{O(l)}H2O(l) | 69.969.969.9 |
Determine the standard entropy, SθS^{\theta}Sθ, of anhydrous magnesium sulfate, MgSO4(s)\text{MgSO}_4\text{(s)}MgSO4(s), in J K−1mol−1\text{J K}^{-1}\text{mol}^{-1}J K−1mol−1.
Give your answer to 3 significant figures.
