A) i) Define bond energy.

• Lattice energy of NaCl, $\Delta H_{L} = -783 \text{ kJ/mol}$ (This is the enthalpy change for forming NaCl(s) from gaseous ions).
• Enthalpy of hydration of Na$^{+}$, $\Delta H_{hyd} [\text{Na}^{+}(\text{g})] = -402 \text{ kJ/mol}$
• Enthalpy of hydration of Cl$^{-}$, $\Delta H_{hyd} [\text{Cl}^{-}(\text{g})] = -377 \text{ kJ/mol}$

The dissolution process is: $\text{NaCl(s)} \longrightarrow \text{Na}^{+}(\text{aq}) + \text{Cl}^{-}(\text{aq})$
This can be broken down into two steps:

1. Breaking the lattice into gaseous ions: $\text{NaCl(s)} \longrightarrow \text{Na}^{+}(\text{g}) + \text{Cl}^{-}(\text{g})$. The enthalpy change for this step is the negative of the lattice energy, $-\Delta H_{L}$.
2. Hydrating the gaseous ions: $\text{Na}^{+}(g) + \text