Engineering Thermodynamics/Third Law

From Wikibooks, open books for an open world
Jump to navigation Jump to search
Engineering Thermodynamics | Thermodynamic Systems | First Law | Second Law | Applications

Third Law of Thermodynamics[edit | edit source]

The Third Law of Thermodynamics extends the definition of Entropy:

Entropy is zero only in a perfect crystal at absolute zero ( 0 kelvin [- 273.15 degree Celsius ]).

The Third Law of Thermodynamics can mathematically be expressed as

lim ST→0 = 0 (1)


S = entropy (J/K)

T = absolute temperature (K)

At a temperature of absolute zero there is no thermal energy or heat. At a temperature of zero Kelvin the atoms in a pure crystalline substance are aligned perfectly and do not move. There is no entropy of mixing since the substance is pure. By -VBM