Lattice Energy
Definition and meaning of Lattice Energy in chemistry.
Lattice energy is the energy required to completely separate one mole of an ionic solid into gaseous ions. It is a key quantitative measure of the strength of the ionic bonds in the crystal lattice.
In more detail
Lattice energy depends on the charges and sizes of the ions in the crystal structure. Higher ionic charges and smaller ionic radii produce stronger electrostatic attractions and higher lattice energies. The Born-Haber cycle uses lattice energy as a key thermodynamic value to calculate the enthalpy of formation of ionic compounds from their elements. Lattice energy is always positive when defined as the energy required to separate the solid, reflecting the energy input necessary to overcome the strong electrostatic forces holding the crystal together.
Key facts
| Definition | Energy required to separate one mole of ionic solid into gaseous ions |
|---|---|
| Field | Physical Chemistry |
| Example compound | NaCl, approximately 786 kJ/mol |
| Depends on | Ionic charge and size (Coulomb's law); higher charge and smaller size increase lattice energy |
Sodium chloride (NaCl) has a lattice energy of approximately 786 kJ/mol, meaning 786 kilojoules of energy must be supplied to convert one mole of solid NaCl into gaseous Na+ and Cl- ions.
Frequently asked questions
Why is lattice energy always positive?
Lattice energy is defined as the energy required to break apart an ionic solid, making it endothermic and always positive. The reverse process, where gaseous ions combine to form solid, releases energy and is negative.
How do you measure lattice energy?
Lattice energy cannot be directly measured experimentally. It is calculated indirectly using the Born-Haber cycle, which combines enthalpy of formation, ionization energy, electron affinity, and other thermodynamic values.