Table 1 shows some enthalpy change data.
| Process | Enthalpy change / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| Mg2+(g)→Mg2+(aq)\text{Mg}^{2+}\text{(g)} \rightarrow \text{Mg}^{2+}\text{(aq)}Mg2+(g)→Mg2+(aq) | −1921-1921−1921 |
| Cl−(g)→Cl−(aq)\text{Cl}^{-}\text{(g)} \rightarrow \text{Cl}^{-}\text{(aq)}Cl−(g)→Cl−(aq) | −364-364−364 |
| Mg2+(g)+2Cl−(g)→MgCl2(s)\text{Mg}^{2+}\text{(g)} + 2\text{Cl}^{-}\text{(g)} \rightarrow \text{MgCl}_2\text{(s)}Mg2+(g)+2Cl−(g)→MgCl2(s) | −2526-2526−2526 |
Use the data in Table 1 to calculate the molar enthalpy change when magnesium chloride dissolves in water.
Use your answer to Part 1 to deduce how the temperature changes when magnesium chloride dissolves in water.
Explain why the enthalpy of hydration of magnesium ions, Mg2+\text{Mg}^{2+}Mg2+, is more negative than the enthalpy of hydration of calcium ions, Ca2+\text{Ca}^{2+}Ca2+.
