What is internal energy?
Thermodynamics as a discipline was formed by the middle of the 19th century. This happened after the discovery of the law on the conservation of energy. There is a definite connection between thermodynamics and molecular kinetics. What is the place in the theory of internal energy? Consider this in the article.
Statistical mechanics and thermodynamics
The original scientific theory of thermal processes was not molecular-kinetic. The first was thermodynamics. It was formed in the process of studying the optimal conditions for the application of heat to work. This happened in the middle of the 19th century, before molecular kinetics gained recognition. Today, both thermodynamics and molecular kinetic theory are used in engineering and science. The latter in theoretical physics is called statistical mechanics. She, along with thermodynamics, explores the same phenomena using different methods. These two theories complement each other. The basis of thermodynamics is made up of two of its laws.Both relate to the behavior of energy and are established empirically. These laws are valid for any substance, regardless of the internal structure. A deeper and more accurate science is considered statistical mechanics. Compared with thermodynamics, it is more complex. It is used in the case when the thermodynamic relations turn out to be insufficient to explain the studied phenomena.
Molecular Kinetic Theory
By the middle of the 19th century, it was proved that along with the mechanical energy, there is an internal energy of macroscopic bodies. It is included in the balance of energetic natural transformations. After the internal energy was discovered, a statement was formulated about its conservation and transformation. While the puck sliding over the ice stops under the influence of friction, its kinetic (mechanical) energy not only ceases to exist, but is transferred to the molecules of the puck and ice. When moving, the irregularities of the surfaces of bodies subjected to friction deform. In this case, the intensity of moving randomly molecules increases. When both bodies are heated, the internal energy increases.It is easy to observe and reverse transition. When water is heated in a closed tube, the internal energy (and its, and the resulting vapor) begins to increase. The pressure will increase, causing the plug to be pushed out. Internal steam energy will cause an increase in kinetic energy. In the process of expanding steam makes work. At the same time, its internal energy decreases. As a result, the steam is cooled.
Internal energy. general information
With the random movement of all molecules, the sum of their kinetic energies, as well as the potential energies of their interactions, is the internal energy. Given the position of the molecules relative to each other and their movement, it is almost impossible to calculate this amount. This is due to the huge number of elements in macroscopic bodies. In this regard, it is necessary to be able to calculate the value in accordance with the macroscopic parameters that can be measured.
The substance is considered to be rather simple in its properties, since it consists of individual atoms, not molecules. To monatomic gases include argon, helium, neon. The potential energy in this case is zero.This is due to the fact that the molecules in an ideal gas do not interact with each other. The kinetic energy of random molecular motion is decisive for internal (U). In order to calculate the U of a monatomic gas of mass m, we need to multiply the kinetic energy of the (average) 1st atom by the total number of all atoms. But it must be borne in mind that kNA = R. Based on the data we have, we get the following formula:U = 2/3 x m / M x RT,where the internal energy is directly proportional to the absolute temperature. All changes in U are determined only by T (temperature), measured in the initial and final state of the gas, and are not directly related to the volume. This is due to the fact that the interaction of its potential energy is 0, and it does not at all depend on other system parameters of macroscopic objects. With more complex molecules, the ideal gas will also have internal energy directly proportional to the absolute temperature. But I must say, in this case the proportionality coefficient will change between U and T. After all, complex molecules perform not only translational movements, but also rotational ones.Internal energy is equal to the sum of these movements of molecules.
What does U depend on?
Internal energy is influenced by one of the macroscopic parameters. This is the temperature. In real gases, liquid and solids, the potential energy (average) in the interaction of molecules is not equal to zero. Although, more precisely, for gases it is much less than the kinetic (average). At the same time for solid and liquid bodies - comparable to it. But the average U depends on V of the substance, because in the period of its change the average distance between molecules changes. From this it follows that in thermodynamics, the internal energy depends not only on temperature T, but also on V (volume). Their value uniquely determines the state of the bodies, and hence the U.
It is difficult to imagine what incredibly large reserves of energy the World Ocean contains. Consider what constitutes the internal energy of water. It should be noted that it is also thermal, because it was formed as a result of overheating of the liquid part of the ocean surface. So, having a difference, for example, of 20 degrees relative to the bottom water, it acquires a value of about 10 ^ 26 J.When measuring currents in the ocean, its kinetic energy is estimated to be about 10 ^ 18 J.
There are global problems that can be put on a global level. These include:
- depletion of reserves of fossil fuels (primarily oil and gas);
- significant environmental pollution associated with the use of these minerals;
- thermal "pollution", plus the whole increase in the concentration of atmospheric carbon dioxide, threatening global climate violations;
- the use of uranium reserves, leading to the emergence of radioactive waste, which have a very negative impact on the livelihoods of all living things;
- the use of thermonuclear energy.
All this uncertainty about the expectation of consequences, which will certainly come, if you do not stop consuming the energy produced in such ways, makes scientists and engineers devote almost all their attention to solving this problem. Their main task is to find the optimal source of energy. It is also important to activate various natural processes.Among them the greatest interest are: the sun, or rather the solar heat, wind and energy in the oceans.In many countries, seas and oceans have long been viewed as an energy source, and their prospects are becoming more and more promising. The ocean is fraught with many secrets, its internal energy is a bottomless wealth of possibilities. The mere fact that how many ways of extracting energy it provides us (such as ocean currents, tidal energy, thermal energy and others), already makes us think about its greatness.