Specific heat of air. Physical properties of substances

The air around us plays an important role in the life of biological organisms inhabiting the planet Earth. But human activity, associated with a variety of technological processes, has identified this substance as a technically important gas. He was thoroughly studied for physical properties. During the experiments, the physical properties of the air, a number of their features and dependencies were revealed.

Difficulty working with air is that it is a non-uniform substance and is a solution from a huge number of components. But still, some kind of stability of its composition is present.

The natural recipe for a vital gas (air) includes a practically stable set of ingredients. To date, they have the following percentage: nitrogen occupies 78 percent, oxygen-20, carbon dioxide-0.03 percent. Steam, other gases and even solid particles occupy about one and a half percent. Specific heat of air depends not only on other physical factors, but also varies depending on the internal content (composition) of the gas.

The collection and analysis of data on the thermodynamic properties of air was spent labor collectives of the world's largest laboratories. These studies have their origin from the end of the XIX century and are actively conducted to this day. Their results are used in the calculation of a variety of energy and air separation plants, devices for the chemical industry and other devices.

Specific heat of air is a quantity that determines the amount of thermal energy that must be spent so that one kilogram of this gas changes its temperature by one degree (kelvin). Given the previously mentioned dependence of this quantity on many factors for engineering purposes, different graphs and tables are created. They indicate how the specific heat of air varies with temperature or humidity.

For a deeper study of this substance, experiments were carried out, for which dry air, purified from carbon dioxide, was used. In the first case, the specific heat at constant pressure (Cp) was determined, in the second case, with a constant volume (Cv) and identical thermometer readings. It is interesting that at 0 ° the Cp value was 0.2402 cal / g · deg, and Cv of the same gas was 0.1713 cal / g · deg. The ratio of these quantities gives the following thermodynamic index, which is of great importance in thermodynamics.

To determine the gas constant (R), calculate the difference in specific heats of the gas under study at constant pressure (Cp) and at a constant volume (Cv). The physical meaning of this quantity is to determine the work of expansion, for example, one kilogram of gas (air) with increasing its temperature by one degree (kelvin).

In previous experiments, the physical properties of dry air were studied. In real practice, account for the percentage content of steam (moisture) in it. Specific heat of air containing a certain amount of water (steam), has its own dependencies and patterns of change.

Wet air has become the subject of a whole trend in physical research, because the vapor content in it affects a whole range of physical and even chemical processes. Living organisms are no exception. The change in air humidity not only affects the comfort of microclimate conditions of the premises (office, shop, laboratory), but also affects the efficiency of employees, the safety of a number of substances and even the operation of certain devices.

Not only a statement of facts, but also a search for various ways to influence the properties of air is the subject of scientific research. They are of great importance in the most diverse fields of human activity, from the chemical industry to the construction of residential premises.