Third law of thermodynamics - Definition and Overview

The third law of thermodynamics was developed by Walther Nernst and is thus sometimes referred to as Nernst's theorem.

This states that the entropy of a system at zero absolute temperature is a well-defined constant. This is because a system at zero temperature exists in its ground state, so that its entropy is determined only by the degeneracy of the ground state.

A special case of this is systems with a unique ground state, such as crystal lattices. The entropy of these systems as defined by Nernst's theorem is zero (since ln(1) = 0).

See also

• Thermodynamics: Thermodynamic entropy, Timeline of thermodynamics, statistical mechanics, and random processes
• Other: Adiabatic process, Ground state