Gavin Howe
The third law of thermodynamics, also known as Nernst's theorem, was formulated by German chemist Walther Nernst between 1906 and 1912. Nernst's theorem states that the entropy of a closed system at thermodynamic equilibrium approaches a constant value when its temperature approaches absolute zero. This law is derived from the statistical-mechanics definition of entropy for a large system. Rudolf Clausius, a 19th-century scientist, is also considered one of the central founders of the science of thermodynamics.
| Characteristics | Values |
|---|---|
| Creator of the third law of thermodynamics | Walther Nernst |
| Years of development | 1906-1912 |
| Alternative name | Nernst heat theorem or Nernst-Simon heat theorem |
| Doctoral student who contributed | Francis Simon |
| Statement of the law in 1912 | "It is impossible for any procedure to lead to the isotherm T = 0 in a finite number of steps." |
| Alternative version | Enunciated by Gilbert N. Lewis and Merle Randall in 1923 |
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What You'll Learn
Walther Nernst formulated the third law
Nernst's formulation of the third law in 1912 was: "It is impossible for any procedure to lead to the isotherm T = 0 in a finite number of steps." This means that it is impossible to reach absolute zero through a finite series of real-world processes. The third law also provides an absolute reference point for determining the entropy of a system at any other temperature.
The third law is derived from the statistical-mechanics definition of entropy for a large system. It is related to the number of accessible microstates, with there typically being one unique state (the ground state) with minimum energy. This is because a system at zero temperature exists in its ground state, so its entropy is determined only by the degeneracy of the ground state.
The third law is not intuitive and was derived empirically as a system's entropy always approached the same minimum value as the absolute temperature was lowered and approached zero. Walther Nernst's work built upon the foundations laid by Rudolf Clausius, considered one of the central founders of the science of thermodynamics.
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Nernst's doctoral student, Francis Simon, contributed
When Simon began working with Nernst in 1920, Nernst had already written a monograph proving, to his satisfaction, that the heat theorem was correct and should be considered a fundamental law of physics. However, many people did not share this conviction, and it was left to Simon to validate the law, which Nernst was starting to lose interest in. Simon's challenge was to prove that, as absolute zero is approached, any system tends towards a state of zero entropy or maximum statistical orderliness. This was because many systems, such as glasses, still exhibited disorder when cooled to extremely low temperatures.
Simon's work with his school provided valuable insights. They investigated systems like ortho-hydrogen, the chemical constant of which suggested the existence of zero-point entropy. Their experiments consistently demonstrated that some ordering always occurs, even at temperatures below zero, bringing the system into agreement with the third law. Additionally, Simon offered an explanation for the peculiar fact that helium remains a liquid under its own vapour pressure, even at absolute zero. He attributed this to the vibration of atoms, which is a consequence of Nernst's theorem.
Simon's contributions to the field of low-temperature physics were significant. In 1936, he produced the first liquid helium using magnetic cooling at a laboratory near Paris. Simon's work in this field was so impressive that it even overshadowed his achievements in proving and elucidating the third law of thermodynamics.
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Rudolf Clausius is a founder of thermodynamics
Rudolf Clausius is considered one of the founders of thermodynamics. Born on January 2, 1822, in Köslin, Prussia (now Poland), Clausius was a German mathematical and theoretical physicist who played a crucial role in establishing theoretical physics as a discipline. He is best known for formulating the second law of thermodynamics, which states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems never decreases. This law was first presented in his famous 1850 paper, "Über die bewegende Kraft der Wärme" ("On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom"), which was published in the Annalen der Physik in the same year.
In this groundbreaking paper, Clausius introduced the concept of entropy, a term he coined from the Greek words "en," meaning "in," and "tropē," meaning "transformation", thus conveying the idea of "content transformation" or "transformation content." He defined entropy as the basic idea of the second law of thermodynamics, summarizing it with the statement, "Heat cannot of itself pass from a colder to a hotter body." This paper made him famous among scientists and laid the foundation for modern thermodynamics.
Clausius' work built upon the earlier principles established by Sadi Carnot in 1824. By restating Carnot's principle concerning the efficiency of heat engines, Clausius provided a more robust basis for the theory of heat. He also contributed to the theory of electrolysis by suggesting that molecules are composed of continually interchanging atoms, a perspective that later served as the foundation for the theory of electrolytic dissociation.
Beyond his work in thermodynamics, Clausius made significant contributions to molecular physics and kinetic theory. In 1865, he published The Mechanical Theory of Heat, in which he provided the first mathematical version of the concept of entropy. Additionally, he deduced the Clausius-Clapeyron relation, which characterizes the phase transition between two states of matter, such as solid and liquid. For his contributions, Clausius received recognition during his lifetime, including an Honorary Membership of the Institution of Engineers and Shipbuilders in Scotland in 1859 and the Copley Medal from the Royal Society of London in 1879.
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The third law changed from fundamental to derived
The third law of thermodynamics, also known as the Nernst heat theorem, was developed by chemist Walther Nernst between 1906 and 1912. The law states that the entropy of a closed system at thermodynamic equilibrium approaches a constant value as the temperature approaches absolute zero.
The third law of thermodynamics changed from a fundamental law to a derived law with the development of statistical mechanics. It is primarily derived from the statistical-mechanics definition of entropy for a large system. This definition states that Ω is the number of microstates consistent with the macroscopic configuration. The counting of states is from the reference state of absolute zero, which corresponds to the entropy of a system at absolute zero.
The third law provides an absolute reference point for determining the entropy of a system at any temperature. It is based on the concept of a perfect crystal, which refers to a pure substance with a well-defined crystalline structure and no impurities. As the temperature of a perfect crystal approaches zero, the vibrations of its individual atoms decrease until they come to a complete stop, resulting in zero entropy.
The third law also has implications for the feasibility of certain processes. According to the law, it is impossible for any procedure to reach absolute zero in a finite number of steps. This means that cooling a system to absolute zero would theoretically require an infinite amount of time or an infinite number of steps.
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The third law is not intuitive
The third law of thermodynamics, formulated in 1912, states that a perfect crystal at absolute zero or zero kelvin has zero entropy. Absolute zero is a temperature at which a thermodynamic system has the lowest energy, and it corresponds to −273.15 °C on the Celsius scale and −459.67 °F on the Fahrenheit scale.
The third law provides an absolute reference point for the determination of entropy at any other temperature. The entropy of a closed system, determined relative to this zero point, is then the absolute entropy of that system. Mathematically, the absolute entropy of any system at zero temperature is the natural log of the number of ground states times the Boltzmann constant kB = 1.38×10−2.
The third law of thermodynamics, also known as the unattainability principle, states that any process cannot reach absolute zero temperature in a finite number of steps and within a finite time. This law is highly intuitive to real-life applications. For example, it is applicable when anyone tries to attain zero temperature and regains temperature from the external environment and other sources.
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Frequently asked questions
The third law of thermodynamics was formulated by Walther Nernst between 1906 and 1912.
The third law of thermodynamics states that the entropy of a closed system at thermodynamic equilibrium approaches a constant value when its temperature approaches absolute zero.
The third law is also known as the Nernst heat theorem, or the Nernst-Simon heat theorem to include the contribution of Nernst's doctoral student Francis Simon.
In simple terms, the third law states that the entropy of a perfect crystal of a pure substance approaches zero as the temperature approaches zero.
An example of the third law of thermodynamics in everyday life is the process of freezing food to preserve it. As the temperature of the food approaches absolute zero, its entropy decreases, which helps to prevent spoilage.
