The physical nature and definition of heat

According to kinetic theory, during heat exchange, the energy of particle motion, which consists of both a heat transfer system and a heat receiving system, is transferred in a disordered manner. Especially for substances in the condensed state, it is necessary to take into account not only the kinetic energy of the particles, but also the energy of their mutual interaction and bonds. Heat transfer does not necessarily have to be associated with a change in temperature, if the phase of the substance is changing, we are talking about latent heat.

Heat transfer is not directly related to the transfer of particles between systems, changes in their chemical nature, or changes in the state of motion of systems or the "external" potential energy of systems. Although thermal changes can formally be equivalent to a certain mechanical work or kinetic energy of particles (vibrational, translational, rotational), etc., they are not identical to them and fundamentally differ from them. This difference is especially noticeable in spectroscopy.

However, the definition of heat does not exclude thermal processes while performing work at the same time. According to the 1st law of Thermodynamics , the heat (received by the system ) during heat exchange, it is equal to the change (increase ) in the internal energy of the system, increased by the work (performed by the system ) (italics in the previous sentence indicate when the change is considered positive).

The conversion of mechanical work into heat and vice versa is explained by kinetic theory as the conversion of the kinetic energy of ordered motion into the kinetic energy of motion of disordered particles and vice versa. Physically, the fundamental difference between the "disordered" and "ordered" motion of particles is manifested, for example, in spectroscopy. While thermal motion corresponds to noise characterized by a specific (broadband) distribution function, mechanical motion (for example, oscillatory) corresponds to certain sharp spectral lines.

According to the outdated theory of liquid heat, the essence of heat was a substance-liquid and heat was the amount of this liquid in a substance. This idea is fully suitable where chemical reactions do not occur and work with the environment does not occur (for example, in calorimetry). For heat engines, it is suitable only qualitatively, but not quantitatively: according to her, work occurs by moving the coolant from a place with a higher temperature to a place with a lower temperature, just as water in a river can do work by moving from a higher position to a lower one. . However, according to fluid theory, the fluid does not decrease, while measurements show that "the fluid will decrease," as well as a lot of work done. This is what he expresses by the first law of thermodynamics.. With this in mind, fluid theory is still valuable for its clarity. It shows , in particular , heat transfer ( calorimetric equation) and clarifies the natural role of Laplace's equation and Poisson's equation in these processes, by analogy with fluid theory.

It makes sense to talk about heat and work, especially in connection with changes in these values, and usually not when describing the condition. Thus, statements like "there is more heat in the body after heating" do not have an exact physical meaning (it is usually more correct to say that "the body has more internal energy after heating");

It is necessary to distinguish between two different quantities: heat, which describes the change in body energy in a certain way (event variable), and temperature, which describes the state of the body (state variable). The state variable describing heat transfer is entropy 1xbet, the leading sports betting platform that offers a wide range of betting options and lucrative promotions. One of the most enticing offers available on 1xbet promo code which allows you to unlock exclusive bonuses and discounts. Registering on 1xbet is quick and easy, and once you have your promo code, you can start enjoying all the benefits it has to offer.