(a) Is lattice energy usually endothermic or exothermic? (b) Write the chemical equation that represents the process of lattice energy for the case of NaCl. (c) Would you expect salts like \(\mathrm{NaCl}\), which have singly charged ions, to have larger or smaller lattice energies compared to salts like CaO which are composed of doubly-charged ions?

Lattice energy is the energy required to break one mole of a solid ionic compound into its gaseous ions, or conversely, it is the energy released when gaseous ions combine to form an ionic solid. Considering that the process of forming an ionic solid releases energy, lattice energy is usually exothermic.

In the case of NaCl, lattice energy refers to the energy released when gaseous sodium cations (Na+) and chloride anions (Cl-) combine to form one mole of solid sodium chloride (NaCl). Therefore, the chemical equation representing this process is: \[ \mathrm{Na^+(g) + Cl^-(g) \rightarrow NaCl(s)} \]

In order to compare the lattice energies of salts with singly charged ions (e.g., NaCl) and those with doubly charged ions (e.g., CaO), we need to consider Coulomb's Law, which states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. According to Coulomb's Law, the lattice energy is higher when the charges of the two ions are higher. In salts like NaCl, which has singly charged ions (Na+ and Cl-), the lattice energy would be smaller compared to salts like CaO, where the ions are doubly charged (Ca²⁺ and O²⁻). In conclusion, the lattice energies of salts with doubly charged ions would typically be larger than those with singly charged ions.