23. Advantages and disadvantages of macroscopic theory of heat phenomena

We have been introduced to the basic laws of the theory of heat phenomena. They are quite simple and very common. They are equally applicable to gases, liquids, solids and even light.

It was defined the Conservation of Energy as a Fundamental Principle. One way to state this principle is "Energy can neither be created nor destroyed". Another approach is to say that the total energy of an isolated system remains constant. The conservation of energy principle is one of the foundation principles of all science disciplines. A little was written about the natural direction of nature's processes.

But along with the advantages of the macroscopic theory of heat processes (thermodynamics) reveals a certain limitation. The common laws of thermodynamics are not enough to calculate any process to the end, or number. In addition to the basic laws, it is necessary to involve a range of experimental data to the theory. For example, it is impossible to find the internal energy even of such a simple system as the ideal gas without using experiments.

It is also impossible to find theoretically a connection between the parameters that characterize the state of the body, in other words, the equation of state. Remember that the Clapeyron equation is established with the help of experimental gas laws.

But that's not the point. Thermodynamics does not reveal the molecular-kinetic nature of heat. Respectively, the deep physical meaning of such notions as temperature, internal energy, and others is not revealed.

The most important problem of finding out the internal structure of all bodies in the scope of thermodynamics cannot even be set.

All these reasons led to the need for a deeper and therefore more complex description of the processes in terms of the microscopic structure of bodies. A molecular-kinetic theory of the structure of the substance was developed.