This question is about energy changes.
a.
[6]
Lattice enthalpies can be determined indirectly using Born-Haber cycles.
The table below shows the energy changes that are needed to determine the lattice enthalpy of magnesium fluoride, MgF2\text{MgF}_2MgF2.
| Energy term | Energy change / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| Enthalpy of formation of magnesium fluoride | −1124-1124−1124 |
| 1st electron affinity of fluorine | −328-328−328 |
| 1st ionisation energy of magnesium | +738+738+738 |
| 2nd ionisation energy of magnesium | +1451+1451+1451 |
| Atomisation of fluorine | +79+79+79 |
| Atomisation of magnesium | +148+148+148 |
(i) The diagram below shows an incomplete Born-Haber cycle that can be used to calculate the lattice enthalpy of magnesium fluoride.
Identify the species, including state symbols, that belong on each of the four dotted lines.
(ii) Calculate the lattice enthalpy of magnesium fluoride, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1.
b.
[4]
The first and second ionisation energies of magnesium, Mg\text{Mg}Mg, and calcium, Ca\text{Ca}Ca, in Group 2 are given in the table below.
| Element | First ionisation energy / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 | Second ionisation energy / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|---|
| Mg\text{Mg}Mg | +738+738+738 | +1451+1451+1451 |
| Ca\text{Ca}Ca | +590+590+590 | +1145+1145+1145 |
- Explain why the first ionisation energy of Mg\text{Mg}Mg is greater than the first ionisation energy of Ca\text{Ca}Ca.
- Explain why the second ionisation energy of Ca\text{Ca}Ca is greater than the first ionisation energy of Ca\text{Ca}Ca.