Third Law of Thermodynamics

During the year 1906, the German chemist Walther Nernst developed the third law of thermodynamics. Walther Nernst received the Nobel Prize in Chemistry in 1920 for this work. As a result, the third law of thermodynamics is also known as Nernst’s theorem or Nernst’s postulate. As can be seen, the third law of thermodynamics states that as the temperature approaches zero, the entropy of a system in thermodynamic equilibrium approaches zero. Alternatively, when the entropy approaches zero, the absolute temperature of any pure crystalline substance in thermodynamic equilibrium approaches zero.

Nernst’s Theorem of Heat (a consequence of the Third Law).

It is impossible for any process, no matter how idealised, to reduce a system’s entropy to absolute zero in a finite number of operations.

Law of Thermodynamics

According to the zeroth law of thermodynamics, if two bodies (A and B) are in thermal equilibrium with another body (third body as C), then these two bodies are also in thermal equilibrium with each other. Because such a conclusion may appear trivial and easy to reach, some may believe it is unworthy of being one of the fundamental laws of thermodynamics. However, because the conclusion drawn from the zeroth law of thermodynamics cannot be reached using the other two basic laws of thermodynamics, and it validates temperature measurement, RH Fowler proposed the zeroth law of thermodynamics in 1931.In reality, the zeroth law was developed more than a half-century after the first and second laws of thermodynamics. However, because the zeroth law should have been developed prior to the first and second laws of thermodynamics, it was given the name zeroth law.

What Is The Third Law of Thermodynamics?

Like the other laws, the third law of thermodynamics is a postulate that is confirmed by its consequences. The observations that led to the postulate’s formulation will not be discussed here.

Nernst stated that at temperatures very close to absolute zero, the entropy change for each chemical or physical transition between condensed phases is equal to zero:

The Nernst heat theorem is another name for this statement. Nernst’s statement was simplified by Planck. He claimed that if the temperature approaches absolute zero, not only the entropy change for processes, but also the actual entropy of each condensed substance, equals zero. This statement expressly states that mixtures are not permitted.

The third law has the important consequence of allowing the absolute entropy of chemical materials (elements and compounds) to be defined (independent of a specific reference state). The absolute entropy of a substance can now be calculated colorimetrically by measuring its heat capacity over the entire temperature range from absolute zero to the desired temperature, as well as the latent heats of phase transitions that occur in this temperature range.

Boltzmann Constant

The Boltzmann constant is an extremely important proportionality factor. It appears in Planck’s law of black-body radiation as well as Boltzmann’s entropy formula. It is also used to calculate the kelvin temperature and the gas constant. The Boltzmann constant is defined as the proportionality constant that shows the relationship between a gas’s thermodynamic temperature and its average relative kinetic energy. The Boltzmann constant has the same unit as entropy, which is energy divided by temperature.

The name is derived from the name of a well-known Austrian scientist, Ludwig Boltzmann. The Boltzmann constant is now one of the seven ‘defining constants’ with precise definitions. This resulted from the 2019 redefinition of SI base units.

These defining constants are used in various combinations to create the seven SI base units. The Boltzmann constant has the value 1.380649 x1023 JK-1.

Alternative Forms of the Third Law of Thermodynamics

According to the Nernst statement of the third law of thermodynamics, a process cannot reduce the entropy of a given system to zero in a finite number of operations.

Merle Randall and Gilbert Lewis, two American physical chemists, stated this law differently: when the entropy of each element (in their perfectly crystalline states)is assumed to be zero at absolute zero temperatures, the entropy of every substance must have a positive, finite value. However, at absolute zero, the entropy can be equal to zero, as in the case of a perfect crystal.

Conclusion

The third law of thermodynamics is also known as Nernst’s theorem or Nernst’s postulate. As can be seen, the third law of thermodynamics states that as the temperature approaches zero, the entropy of a system in thermodynamic equilibrium approaches zero. However, because the conclusion drawn from the zeroth law of thermodynamics cannot be reached using the other two basic laws of thermodynamics, and it validates temperature measurement, RH Fowler proposed the zeroth law of thermodynamics in 1931. Like the other laws, the third law of thermodynamics is a postulate that is confirmed by its consequences. The third law has the important consequence of allowing the absolute entropy of chemical materials to be defined ( independent of a specific reference state).