Where is thermodynamics used?

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The third law of thermodynamics

The measurements of chemical reactions between pure, crystallized solids showed that the change in entropy tends towards zero when approaching absolute zero:

Legend
-Entropy of reaction
-absolute temperature

The equation is called Nernst's heat theorem, whereby originally the heat capacities of the reaction participants were actually measured.

The reaction entropies of the reaction participants can also be inserted into Nernst's heat theorem:

Legend
-stoichiometric coefficients of the starting and end materials
-molar entropies of the starting and end materials

This means that either the molar entropies of the reactants disappear as they approach absolute zero or they all have the same entropy value.

A formulation of the third law of thermodynamics relates to Nernst's heat theorem:

theorem
The value zero can be set for the entropy of all chemical substances that are regarded as ideally crystallized substances at absolute zero. Every chemical substance then has a certain positive entropy.

Another formulation of the third law of thermodynamics is:

theorem
The third law states that there is no process with which it is possible to reach absolute zero in an infinite number of steps.

Since there is no ideally crystallized solid, the absolute zero point cannot be reached either.

At absolute zero there may only be one implementation option (micro-state):

Legend
-Boltzmann constant
-thermodynamic probability

The entropy is then zero.

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