The third law of thermodynamics states that the entropy of a system in a perfect crystalline state is zero, as the temperature approaches zero Kelvin.
Molecular motion decreases with temperature and a pure substance may form a crystal with an uninterrupted lattice structure as , that is, a crystal with a unique configuration. The equation for statistical entropy is:
where is the number of ways to achieve the configuration of the system.
A perfect crystal is one in which every atom, ion, or molecule is arranged in an orderly and repeating pattern with no defects, distortions, or irregularities. This perfect arrangement extends infinitely in all directions, meaning that the crystal lattice is flawless. Since there is only one way to arrange the configuration of a perfect crystal, and