Lattice Energy Calculator

Lattice Energy Calculator

The Lattice Energy Calculator estimates the lattice energy of ionic compounds using the Kapustinskii equation. Lattice energy is the energy required to separate one mole of an ionic solid into its constituent gaseous ions.

$$U = K \cdot \frac{v \cdot |z^+| \cdot |z^-|}{r^+ + r^-} \cdot \left(1 - \frac{d}{r^+ + r^-}\right)$$

where $K = 1.202 \times 10^{-4}$ J·m/mol, $d = 3.45 \times 10^{-11}$ m, $v$ is the number of ions in the empirical formula, $z^+$ and $z^-$ are ion charges, and $r^+$ and $r^-$ are ionic radii in meters.

Example: NaCl has $z^+ = +1$, $z^- = -1$, $r^+ = 102$ pm, $r^- = 181$ pm, and $v = 2$. The Kapustinskii equation gives a lattice energy of approximately 746 kJ/mol. For CaO with doubly charged ions, the lattice energy is much higher (around 3430 kJ/mol).

Higher ion charges and smaller ionic radii both increase lattice energy. This trend explains why divalent ionic compounds like MgO and CaO have very high lattice energies.

Related tools: Ionic Strength Calculator, Cubic Cell Calculator, and Electronegativity Calculator.