The Nernst heat theorem was formulated by Walter Nernst early in 20th century and was used in development of third law of thermodynamics.
Theorem- The Nernst theorem says that as absolute zero is approached, the entropy change ΔS for a chemical or physical transformation approaches 0. This can be expressed mathematically as follows-
Above equation is modern statement of theorem. Another way of looking at theorem is to start the definition of Gibbs free energy (G). G = H – TS , where H stands for enthalpy.
Graph of energies at low temperature
Limitations of Nernst heat theorem
1. As there exist no gas at absolute zero, Nernst heat theorem could not applied to gases at same time it could not be applied to liquids due to certain valid reasons.
2. Nearest heat theorem is applicable to solids only.