How is the theory of thermodynamics described
History of Thermodynamics
|I. Basics of thermodynamics|
The thermometer was developed in the 17th century. This finally made it possible to measure temperatures precisely. In order to be able to use it consistently, temperature scales were introduced by Gabriel Fahrenheit (1686-1736), Ren Antoine Ferchault de R aumur (1683-1757), Anders Celsius (1701-1777) and by Lord Kelvin (1824-1907). For example the Celsius, Kelvin and Fahrenheit scales. The thermometer laid the foundation for thermodynamics.
Many of the scientists of the time, such as Robert Boyle (1627-1691), Edm Mariotte (approx. 1620 to 1684) as well as Louis Gay-Lussac (1778-1850) carried out numerous experiments and empirically formulated gas laws that describe the relationships between pressure, temperature and Show the volume of a gas. In their experiments, they used what were then known as permanent gases, which behaved almost like ideal gases. These gas laws were later summarized and generalized by many researchers so that they could also be applied to real gases. One of them was Amadeo Avogadro (1776-1856). He was also the first to distinguish between atoms and molecules.
In 1884 Lord Kelvin introduced the absolute temperature scale. In this way, the gas pots were brought to a uniform temperature classification and could thus be compared and combined with one another.
At the end of the 17th century, a connection between heat and work was already being discussed. For a long time the so-called Thermal theory"by Joseph Black (1728-1799). He was the first to distinguish precisely between the amount of heat and temperature. The terms also refer to him Heat capacity and latent heat back.
Many phenomena (e.g. the temperature equalization when a cold and a warm body touch) could be caused by the supposedly existing substance caloriqueIt was assumed that it is an elastic liquid in which the individual particles repel each other and which should stick to bodies with different preferences.
Jean Baptiste Joseph Fourier (1768-1830) established laws that mathematically describe the spread of heat. These are still valid today. To do this, he used new techniques that were also enriching for the mathematics of the time.
Pi rre Simon Laplace (1749-1827) derived equations of state for gases from the heat substance theory, which are also still valid today.
James Watt (1736-1819) and Sadi Carnot (1796-1832) dealt with the efficiency of heat engines. Although Carnot also assumed that the amount of thermal substance would be retained, he found the correct formula, which only depends on the temperatures of two heat accumulators.
However, the frictional heat that arises when bodies rub against one another is not sufficiently explained by the presence of a heat substance. Benjamin Thompson (1753-1814) (later Lord Rumford), studied the heat generated when drilling cannon barrels. He found that this heat is roughly proportional to the mechanical work done while drilling. He concluded from this that it could therefore not possibly be a question of the outflow of a heat substance that had previously been in the barrel of the cannon. Nowadays his argument is seen as evidence against the existence of a heat substance and for the equality of heat and mechanical energy. For a long time, however, some supporters of the thermal substance theory could not be dissuaded from their mistaken belief.
When the new theory gained general acceptance, the law of conservation of energy was also reformulated:"In a thermodynamic process no energy is lost, but mechanical work and heat are converted into one another" (see 1st law of thermodynamics). Mainly involved in the reformulation were the scientists Julius Mayer (1814-1878), James Prescott Joule (1818-1889) and Hermann von Helmholtz (1821-1894).
It was soon recognized, however, that mechanical work can be converted completely into heat, but not vice versa. Rudolf Clausius (1822-1888) found out that the law of conservation of energy is insufficient to explain all thermodynamic processes. Heat, for example, always flows from the hotter to the cooler body without any external compulsion, but never the other way around, even though this would not violate the law of conservation of energy. Therefore the so-called 2nd law of thermodynamics was formulated: "When no work is done, heat can only flow from warm to cold".
More generally speaking, this means that the entropy always increases in an isolated system and that it only remains the same in the case of reversible processes.
The newly formulated variable, entropy, is, like pressure, energy and temperature, a variable that describes the state of a gas. Clausius was able to grasp it mathematically, but its physical meaning was unclear to him. He first developed the so-called "kinetic gas theory" with James Clerk Maxwell (1831-1879), Lord Kelvin and Ludwig Boltzmann (1844-1906). They assumed that gases consist of individual free-flying atoms and that they collide with one another in a completely elastic manner (see ideal gases). From this microscopic model and simple statistical reports on the distribution of the gas particles in the space available to them, it was possible to use the already empirically found gas laws (by Gay-Lussac and Boyle-Mariotte) and the law of conservation of energy (the 1st law of thermodynamics) derive.
Boltzmann finally managed to come up with a microscopic explanation of entropy. In his deliberations, he divided the possible locations of the gas particles into individual cells. With this model he found out that the logarithm of the distribution of the particles on the individual cells, whatever corresponds to a certain state, is proportional to its entropy. The constant used in this equation was named the Boltzmann factor in his honor.
He also found that the entropy in isolated systems and thus in the universe, always grows or at least remains the same. Mathematically he proved this with the fact that the probability of order, and thus the decrease in entropy, is vanishingly small.
This was the first time that a physical law was described that had a statistical character. This sparked a lot of discussion among the other scientists of the time. He was even attacked from two sides:
Some disapproved of his atomic hypothesis. Although this had been reintroduced into chemistry by Dalton, there was strong resistance to the existence of atoms on the part of physicists, mainly from Ernst Mach (1838-1916) and Wilhelm Friedrich Ostwald (1853-1932). They were of the opinion that in chemistry and physics you don't need atoms and you should drop them as unproven and unprovable hypotheses.
The other side thought the irreversibility hypothesis was nonsense. Henri Poincar (1854-1912) and Ernst Zermelo (1871-1953) tried to justify that Boltzmann's derivation of the 2nd law from his microscopic particle theory without time direction is wrong.
Today Boltzmann is right on both points and the theories and formulas he developed are groundbreaking for today's physics and today's chemistry.
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