Why are lattice enthalpies always endothermic?

Lattice enthalpies are always endothermic because they represent the energy required to break a lattice into its constituent ions.

Lattice enthalpy is a measure of the strength of the forces between the ions in an ionic solid. It is defined as the energy required to break one mole of a solid ionic compound into its gaseous ions under standard conditions. This process requires an input of energy to overcome the strong electrostatic forces of attraction between the oppositely charged ions in the lattice. Therefore, lattice enthalpies are always endothermic.

The magnitude of the lattice enthalpy gives an indication of the strength of the forces holding the ions together. The larger the lattice enthalpy, the stronger the forces and the more energy is required to break the lattice apart. This is why ionic compounds with high lattice enthalpies tend to have high melting and boiling points.

The value of the lattice enthalpy is influenced by the charge on the ions and the size of the ions. The greater the charge on the ions, the stronger the forces of attraction and the larger the lattice enthalpy. Similarly, smaller ions are able to get closer together, resulting in stronger forces of attraction and a larger lattice enthalpy.

In summary, lattice enthalpies are always endothermic because they represent the energy required to overcome the strong electrostatic forces of attraction between the ions in an ionic lattice. The magnitude of the lattice enthalpy gives an indication of the strength of these forces and is influenced by the charge and size of the ions.