A third law of thermodynamics addresses the relationship between the entropy and an absolute reference point to determine it, he being the absolute zero. She also states that if a heat engine were able to reach absolute zero temperature, all of its heat would be converted into work, making it a perfect machine. This law is calculated based on the limit of entropy, where the temperature tends to zero.
Read too: What are the most used thermometric scales in Physics?
Topics of this article
- 1 - Summary of the third law of thermodynamics
- 2 - What does the third law of thermodynamics say?
-
3 - Formula of the third law of thermodynamics
- entropy formula
- 4 - Applications of the third law of thermodynamics
- 5 - How did the third law of thermodynamics come about?
- 6 - Laws of thermodynamics
Summary on the third law of thermodynamics
The third law of thermodynamics was formulated by physical chemist Walther Nernst, being derived from the other laws of thermodynamics, according to statistical mechanics.
The third law of thermodynamics states that it is impossible to reach absolute zero.
Scientists have managed to reach temperatures close to absolute zero, but have not yet reached it.
Entropy is the organization of molecules in a system.
The laws of thermodynamics are the zeroth law, first law, second law and third law.
The zeroth law of thermodynamics studies the thermal equilibrium between different bodies.
The first law of thermodynamics studies the conservation of energy in thermodynamic systems.
The second law of thermodynamics studies heat engines and entropy.
The third law of thermodynamics studies absolute zero.
What does the third law of thermodynamics say?
The third law of thermodynamics, known as Nernst's theorem or Nernst's postulate, is a law developed by the physical chemist Walther Nernst (1864 -1941), between 1906 and 1912, which makes up the set of laws of thermodynamics.
In 1912, Nernst enunciated the third law of thermodynamics as:
It is not possible, by any finite series of processes, to reach absolute zero temperature.|1|
According to this law, when we approach a system to the temperature of absolute zero in Kelvin, the entropy (degree of disorder of a system) will have its lowest value, causing all the processes involved to cease their activities, making it possible to identify the point of reference in which it is possible to determine the entropy. In the case of Thermal machines, upon reaching absolute zero, they would be able to convert all of their Thermal energy (heat) in work, without losses.
For a better understanding, the concept of entropy is introduced, in the second law of thermodynamics, as the degree of movement and vibration of the molecules of a system; the greater the possibility of movement, the greater the entropy.
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Formula of the third law of thermodynamics
\(\stackrel{lim\ ∆S=0}{\tiny{T→0}}\)
\(\stackrel{lim\ }{\tiny{T→0}}\) is the limit where the temperature tends to zero.
\(∆S\) is the entropy change of the system, measured in \([J/K]\).
T is the temperature, measured in Kelvin \([K]\).
entropy formula
\(∆S=\frac{∆Q}T\)
\(∆S\) is the entropy change of the system, measured in \([J/K]\).
\(∆Q\) is the change in heat, measured in Joules \([J] \).
T is the temperature, measured in Kelvin \([K] \).
Applications of the third law of thermodynamics
Absolute zero has never been reached in laboratories, making the third law of thermodynamics a theoretical law, therefore, there are no applications of it. However, if this temperature were reached, the heat engines would have a 100% efficiency, and all their heat would be converted into work.
Read too: How to calculate the efficiency of heat engines
How did the third law of thermodynamics come about?
Between 1906 and 1912, the physical chemist Walther Nernst developed the third law of thermodynamics, he was also responsible for research in the fields of electrochemistry It is photochemistry, providing a major advance in the study of physicochemical.
Based on his entropy studies, Walther Nernst proposed that it only occurs in perfect crystals, however, later, he would verify that, in fact, the temperature of absolute zero does not even exist, but also that, if the system is close to this temperature, a minimum entropy value could be obtained.
Since that time, scientists have been trying to obtain this temperature, reaching levels closer and closer to zero. Based on that, they realized that it can only be attainable in gases.
With the development of statistical mechanics, the third law of thermodynamics became a law derived from the basic laws, unlike the other laws that continue to be fundamental, because they have an experimental basis that supports them.
laws of thermodynamics
The laws of thermodynamics deal with the relationships between pressure, volume, and temperature with heat, energy, and other physical quantities. They are composed of four laws: zero law, first law, second law and third law.
Zeroth law of thermodynamics: states that bodies at different temperatures will exchange heat until they reach the thermal balance.
first law of thermodynamics: states that the change in internal energy of a thermodynamic system is given by the difference between the work done by the system and the change in heat it absorbed.
second law of thermodynamics: states that it is impossible to create a machine capable of converting all its heat into work. Furthermore, she enunciates entropy as the degree of disorder in a system.
third law of thermodynamics: states that it is impossible to reach absolute zero.
Note
|1| quote from the book Basic physics course: fluids, oscillations and waves, heat (vol. 2).
By Pamella Raphaella Melo
Physics Teacher
Would you like to reference this text in a school or academic work? Look:
MELO, Pamela Raphaella. "Third Law of Thermodynamics"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/terceira-lei-da-termodinamica.htm. Accessed on August 4, 2023.
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