For several centuries, physicists have assumed that temperature is determined by the presence of an invisible and imponderable caloric substance in gases. Many theories have been put forward to explain its movement within matter and between different objects. Only M. V. Lomonosov was able to explain the real nature of matter by creating the molecular-kinetic theory of gases. In his reasoning and calculations, he managed to prove that there is no caloric in nature. The temperature depends on the speed of the chaotic movement of molecules. He introduced the concept of internal energy, and also explained how it changes in a real process.
What arguments did M. V. Lomonosov to prove the molecular-kinetic theory of gases
Having expressed for the first time the assumption that no caloric exists in nature, he met with powerful resistance from venerable scientists of that period. They all recognized the presence of caloric, but the novice researcher did not. Thenat one of the meetings with German and English physicists the following was said: “Dear teachers. Where did the caloric in the cow's body come from? She ate the cold grass, and then her body warmed up because there was a change in internal energy in her insides. Where did it come from? And the origin of heat in the body is explained by the fact that the grass has chemical energy, which the body of the animal has converted into this heat. This means that we are observing the phenomenon of the transition of energy from one state to another. He was listened to and asked dozens of questions. As a result of the discussion, the law of energy change was also formulated (it is also called the law of conservation of energy), which was recognized by all those present. Later, a small collection of hypotheses was published, which was the first edition where the molecular-kinetic theory of gases was recognized.
What did the theory of M. V. Lomonosov
Today it seems that everything is logical in thermodynamics. But it should be remembered that more than 250 years have passed from the first assumptions to the present day. The French researcher J. Charles discovered the law of proportionality of pressure growth with increasing gas temperature. He then explained the change in the internal energy of a gas when heated. I came up with my own formula. His research was continued 20 years later by Gay-Lussac, who investigated the heating of a gas at constant pressure. He observed how a piston placed inside a glass cylinder changes its position when heated and cooled. Here he came close to the discovery of the concept of gasconstant. He did not take advantage of the research that Robert Boyle had done 140 years earlier. Only the work of Mariotte, carried out later and formulated in the Boyle-Mariotte law, helped Benoit Paul Emile Clapeyron to formulate the first concept of the ideal gas equation of state.
After 40 years, D. I. Mendeleev supplemented the equation of state with the results of his research. Now the Klaiperon-Mendeleev law is the basis for thermodynamicists around the world. It mathematically determines the change in internal energy from the temperature of the gas. The discoveries of the basic laws were also confirmed by practice. Heat engines were created that operate on the thermodynamic cycles of Otto, Diesel, Trinkler and other scientists.
A few words about the law of the ideal gas state
pV=mRT
Today, when deriving any dependencies, the ideal gas equation of state is used. No one is confused by the parameters included in it, which have well-defined concepts. The conclusions from the basic gas law give another important formula characterizing the change in internal energy:
dU=cvDT,
here dU is the differential change in internal energy, and cv is the heat capacity of the gas at constant volume. As a result of reasoning about the nature of the gas constant R, it was found that it characterizes the workgas at constant pressure.
