Explain why the lattice energy and the energy of crystallization of a substance differ in sign but are equal in magnitude.

Lattice energy is energy evolved when a crystal lattice is formed. Crystalization energy refers to energy supplied to collapse the lattice structure.

Explanation:

The lattice energy of an ionic crystal is defined in as the change in energy of the system of atoms and molecules when a crystal is formed from the free ionic forms of the components in the gas phase. It can also be defined as the necessary energy to separate ions of a mole of an ionic crystal as gaseous ions from each other by infinite distances.

The strength of ionic compounds is measured by the magnitude of lattice energy. It is the energy released when one mole of an ionic compound is formed. This means when the individual ions of the compound come together to form the crystal lattice, they need a lesser energy to remain together, hence energy is released, the energy released is called the lattice energy. The bond force between ions of opposite charge is strongest when the ions are small.

Similarly, the crystalization energy is the energy required maintain the crystal structure of the compound. It is also the energy that must be supplied for the crystal structure structure to collapse. Hence its sign is positive.

While lattice energy deals with energy evolved when ions come together to form a crystal, crystallization energy deals with energy absorbed to separate the ions and collapse the crystal structure