The first and second law of thermodynamics

Before considering the first and second principles of thermodynamics, it is necessary to determine what exactly is meant by the term "thermodynamics". In this case, the word speaks for itself: it is easy to define the other two - "thermo" and "dynamics". When translated from Greek, "heat, temperature" and "strength, movement, change" are obtained. In other words, thermodynamics is one of the branches of physics that studies the features of the transformation of heat into other forms of energy and vice versa. In this case, the thermal motion of the objects of the microworld (atoms, molecules, particles) is not included in the mentioned section and is studied in other fields of science. Thermodynamics deals with whole macrosystems, for which volume, pressure, etc. are characteristic.

This science is based on some basic features (zero, first, second law of thermodynamics) taken as postulates. They were determined experimentally and confirmed by theoretical calculations. The relationship between them is only indirect, since it is impossible to directly derive one origin from another.

There are four origins - from zero to the third. We indicate the meaning of each of them. The zero-point principle of thermodynamics asserts that any system tends to thermodynamic equilibrium, so when the external influence disappears, a balance finally arises. In it, an isolated system can be unlimited time.

One of the main is the first law of thermodynamics. It was first formulated in the 19th century. In fact, it is the law of conservation of energy applied to the thermodynamic processes occurring in macrosystems. By the way, often with the help of this postulate, the possibility of the existence of a perpetual motion is denied , since for the performance of work it is necessary to inform the system from the outside with additional energy. According to him, in a closed isolated system, the energy value always remains unchanged.

The second law of thermodynamics is familiar to everyone from childhood. According to him, the heat energy can be naturally transmitted in only one direction - from a warmer body to a less heated one. For example, this is why it seems cold in the winter, as the ambient temperature is lower than that of the human body, which causes heat emission. The second law of thermodynamics is one of the most famous. One of its consequences indicates that the whole internal energy of the system can not be completely transformed into useful work. Interestingly, the second law of thermodynamics is mathematically unprovable. By setting up a multitude of experiments, this regularity was derived, subsequently adopted as an axiom.

What is one of the aspects that characterize the second law of thermodynamics? Entropy! This term in Greek means "transformation". The entropy is characteristic of any thermodynamic system and is a function of the state. In general, we can assume that the entropy indicates the desire of any system to be disordered. R. Clausius, who proposed this term for thermodynamic processes, gave an example of an example with freezing water: imagine water that is in the liquid state at the boundary of zero degrees Celsius. It is necessary for her to report a portion of external energy sufficient to disturb the equilibrium, as the liquid passes into a solid state (ice). At the same time, due to the internal change in the structure, a part of the energy is released. In this case we are talking about a reversible process. Accordingly, the change in entropy is the ratio of the total amount of thermal energy to the absolute value of the temperature. One of the consequences indicates that in closed systems without external influence the value of entropy increases.