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The 'laws of thermodynamics', in principle, describe the specifics for the transport of heat and work in thermodynamic processes. Since their conception, however, these laws have become some of the most important in all of physics and other branches of science connected to thermodynamics. They are often associated with concepts far beyond what is directly stated in the wording.

Contents

History

Overview

Zeroth law

First law

Second law

Third law

Combined law

Tentative fourth laws or principles

Extended interpretations

See also

References

Further reading

External links

History

The first established principle of thermodynamics (which eventually became the Second Law) was formulated by Sadi Carnot in 1824. By 1860, as found in the works of those as Rudolf Clausius and William Thomson, there were two established "principles" of thermodynamics, the first principle and the second principle. As the years passed, these principles turned into "laws." By 1873, for example, thermodynamicist Willard Gibbs, in his “Graphical Methods in the Thermodynamics of Fluids”, clearly stated that there were two absolute laws of thermodynamics, a first law and a second law. Presently, there are a total of four laws. Over the last 80 years or so, occasionally, various writers have suggested adding Laws, all of which are far from unanimously accepted.

Overview

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★ Zeroth law of thermodynamics
:
★ :$A\; sim\; B\; wedge\; B\; sim\; C\; Rightarrow\; A\; sim\; C$
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★ First law of thermodynamics
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★ :$mathrm\{d\}U=delta\; Q-delta\; W,$
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★ Second law of thermodynamics
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★ :
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★ Third law of thermodynamics
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★ : $T$
ightarrow 0, S
ightarrow C
:
★ Onsager reciprocal relations - sometimes called the ''Fourth Law of Thermodynamics''
:
★ : $mathbf\{J\}\_\{u\}\; =\; L\_\{uu\},$
abla(1/T) - L_{ur},
abla(m/T) !;
:
★ : $mathbf\{J\}\_\{r\}\; =\; L\_\{ru\},$
abla(1/T) - L_{rr},
abla(m/T) !.

Zeroth law

Main articles: Zeroth law of thermodynamics

When two systems are put in contact with each other, there will be a net exchange of energy between them unless or until they are in thermal equilibrium, that is they contain the same amount of thermal energy for a given volume (say, 1 cubic centimetre, or 1 cubic inch.) While this is a fundamental concept of thermodynamics, the need to state it explicitly as a law was not perceived until the first third of the 20th century, long after the first three laws were already widely in use, hence the zero numbering. The Zeroth Law asserts that thermal equilibrium, viewed as a binary relation, is an equivalence relation.

First law

Main articles: First law of thermodynamics

More simply, the First Law states that energy cannot be created or destroyed; rather, the amount of energy lost in a steady state process cannot be greater than the amount of energy gained.
This is the statement of conservation of energy for a thermodynamic system. It refers to the two ways that a closed system transfers energy to and from its surroundings - by the process of heating (or cooling) and the process of mechanical work. The rate of gain or loss in the stored energy of a system is determined by the rates of these two processes. In open systems, the flow of matter is another energy transfer mechanism, and extra terms must be included in the expression of the first law.
The First Law clarifies the nature of energy. It is a stored quantity which is independent of any particular process path, i.e., it is independent of the system history. If a system undergoes a thermodynamic cycle, whether it becomes warmer, cooler, larger, or smaller, then it will have the same amount of energy each time it returns to a particular state. Mathematically speaking, energy is a state function and infinitesimal changes in the energy are exact differentials.
All laws of thermodynamics but the First are statistical and simply describe the tendencies of macroscopic systems. For microscopic systems with few particles, the variations in the parameters become larger than the parameters themselves, and the assumptions of thermodynamics become meaningless. The First Law, i.e. the law of conservation, has become the most secure of all basic laws of science. At present, it is unquestioned.

Second law

Main articles: Second law of thermodynamics

In a simple manner, the Second Law states that 'energy systems have a tendency to increase their entropy' (heat transformation content) rather than decrease it.
A way of looking at the Second Law for non-scientists is to look at entropy as a measure of chaos. So, for example, a broken cup has less order and more chaos than an intact one. Likewise, solid crystals, the most organised form of matter, have very low entropy values; and gases, which are highly disorganised, have high entropy values.
The entropy of a thermally isolated macroscopic system never decreases (see Maxwell's demon). However, a microscopic system may exhibit fluctuations of entropy opposite to that dictated by the Second Law (see Fluctuation Theorem). In fact, the mathematical proof of the Fluctuation Theorem from time-reversible dynamics and the Axiom of Causality constitutes a proof of the Second Law. In a logical sense the Second Law thus ceases to be a "Law" of physics and instead becomes a theorem which is valid for large systems or long times.
Stephen Hawking described this using time as an entropy base. For example, when time moves in a forward direction and one, say, drops a cup on the floor, smashing the cup, no matter what happens, in our universe, one will never see the cup reform. Cups are breaking all the time, but never reforming. Since the Big Bang, the entropy of the universe has been on the rise, and so the Second Law states that this process will continue to increase.

Third law

Main articles: Third law of thermodynamics

The Third Law says that this constant is in fact zero. As the temperature approaches zero, the probability that the system, however complex, sits in its unique quantum ground state approaches one. The entropy of any unique state is zero, so the entropy approaches zero. More rigorously, if the system happens to have half-integer net spin, there are two degenerate ground states, related by time-reversal symmetry, so the dimensionless entropy approaches the natural log of two. However, that is the entropy for the whole system, and is negligible on the scale of any macroscopic system. Basically, no system can reach absolute zero.

Combined law

Main articles: Combined law of thermodynamics

Aside from the established four basic laws of thermodynamics described above, there is also the 'combined law of thermodynamics'. The combined law of thermodynamics is essentially the first and second laws subsumed into the following single concise mathematical statement:^[1][2]
:$dE\; -\; TdS\; +\; pdV\; le\; 0.$
Here, E is energy, T is temperature, S is entropy, p is pressure, and V is volume.

Tentative fourth laws or principles

In the late 19th century, thermodynamicist Ludwig Boltzmann argued that the fundamental object of contention in the life-struggle in the evolution of the organic world is 'available energy'. Since then, over the years, various thermodynamic researchers have come forward to ascribe to or to postulate potential 'fourth laws of thermodynamics'; in some cases, there are even fifth or sixth laws of thermodynamics supposed. The majority of these tentative fourth law statements are attempts to apply thermodynamics to evolution. Most fourth law statements, however, are speculative and far from agreed upon.
The most common proposed Fourth Law is the Onsager reciprocal relations. Another example is the maximum power principle as put forward initially by biologist Alfred Lotka in his 1922 article ''Contributions to the Energetics of Evolution''.^[3] Most variations of hypothetical fourth laws (or principles) have to do with the environmental sciences, biological evolution, or galactic phenomena.^[4]

Extended interpretations

The laws of thermodynamics are sometimes interpreted to have a wider significance and implication than simply encoding the experimental results upon which the science of thermodynamics is based. See, for example:

★ Principles of energetics

★ Heat death

See also

★ Conservation law

★ Laws of science

★ Philosophy of thermal and statistical physics

★ Table of thermodynamic equations

★ Thermodynamics

References

1. Combined Law of Thermodynamics - Wolfram's World of Science
2. Bioenergetics, 2nd Ed., Lehninger, Albert, L., , , , 1973, ISBN 0-8053-6103-0
3. A.J.Lotka (1922a) 'Contribution to the energetics of evolution' [PDF]. Proc Natl Acad Sci, 8: pp. 147–51.
4. Morel, R.E. ,Fleck, George. (2006). "Fourth Law of Thermodynamics" ''Chemistry, Vol. 15'', Iss. 4

Further reading

★ Goldstein, Martin, and Inge F., 1993. ''The Refrigerator and the Universe''. Harvard Univ. Press. A gentle introduction.

External links

★ 10+ Variations of the 0th Law

★ 30+ Variations of the 1st Law

★ 110+ Variations of the 2nd Law

★ 20+ Variations of the 3rd Law

★ 15+ Variations of the 4th Law

★ A Proposed 5^th Law of Thermodynamics