Complete the table with ticks ($\checkmark$) to show whether each energy change, under standard conditions, is always positive, always negative, or may be either positive or negative: electron affinity; enthalpy change of atomisation; ionisation energy; lattice energy.
The Born-Haber cycle for magnesium chloride is shown. Explain why $\Delta H_4$ is greater than $\Delta H_3$.
What are the names of the enthalpy changes $\Delta H_6$ and $\Delta H_7$?
Chlorine is in Group $17$. Suggest the trend in the first electron affinity of the elements in Group $17$. Explain your answer.
The equation for the formation of magnesium oxide from its elements is shown: $\text{Mg}(s) + \tfrac{1}{2}\text{O}_2(g) \rightarrow \text{MgO}(s)$, $\Delta H^\circ = -602\,\text{kJ mol}^{-1}$. Use the equation together with the data in the table to calculate $\Delta G^\circ$ for the reaction at $25^\circ\text{C}$.