GASES

From Big Medical Encyclopedia

GASES — substances, aggregate state to-rykh is characterized by the fact that distances between molecules in comparison with their sizes are so big that molecules are not the connected or poorly connected intermolecular forces and move freely, filling all volume provided to them. Unlike G., in liquids and solids «packaging» of molecules of substance is more dense and intermolecular interaction are respectively stronger.

Many substances can be transferred to gaseous state by the corresponding selection of pressure and temperature. So, e.g., with a pressure of 1 at and t ° 100 ° water turns into gaseous state (water vapor). Transition temperatures of nek-ry substances from liquid to gaseous state (and back) with an atmospheric pressure are specified in tab. 1.

Key parameters of G. (pressure, volume and temperature) are caused by quantity of particles in unit volume, a mean motive energy of progress of a molecule, etc. Connection between them is established by the molecular kinetic theory based on M. V. Lomonosov's ideas developed by Boltzmann (L. Boltzmann, 1844 — 1906), Klauzius (R. Clausius, 1822 — 1888), Maxwell (J. Page of Maxwell, 1831 — 1879), etc. In this theory of G. are considered as statistical set of randomly moving and it is elastic the unbound particles colliding among themselves.

Gas, intermolecular interaction of particles to-rogo as well as its own volume, it is possible to neglect, is called ideal. For practical calculations use the equation of a condition of ideal G. (Klapeyron's equation — Mendeleyeva) describing a ratio between pressure P, volume of this mass of gas V and absolute temperature of T:

PV = M/μ RT, where M — the mass of gas in kg, μ — the mass of one kilomole, R — a universal gas constant (R = 8,31*10 3 J / kmol*grad).

Klapeyron's equation — Mendeleyeva generalizes gas laws of Boyle — Marriott (at a constant temperature the volume of this mass of gas is inversely proportional to pressure) and Gay-Lussac (with a constant pressure the volume of this mass of gas is directly proportional to absolute temperature). Follows from the equation also that at an identical temperature and pressure of 1 mol of any ideal gas occupies the equal volume (24,414 l) and contains identical number of molecules (Avogadro's law). Klapeyron's equation — Mendeleyev is used also for the real G. which are in the conditions close to ideal G. (with low pressures, not above atmospheric), and temperatures, enough far from a point of their liquefaction.

Usually for real G., and also for the vapors far from saturation, use the equation Vander-Vaalsa:

where an and b — the constants depending by nature this G.: size and considers forces of an attraction between molecules, b — the volume of particles. Values and and b for nek-ry gases are given in tab. 2.

, being ratio of mixture from the diverse, chemically not interacting G., it is characterized by partial pressure, i.e. pressure, a cut would have this G., occupying the volume equal to the volume of mix at the same temperature. Total pressure of mix of ideal G. equals to the sum of their partial pressures (Dalton's law). Solubility in mix G. is proportional to the partial pressure of each of gases (Henry's law).

In G.'s nature meet as in a stand-at-ease, making the atmosphere of Earth, and in dissolved — in waters of the World Ocean — or absorbed in rocks.

Atmosphere (see) is in a condition of constant exchange with firm and liquid covers of Earth and with the biosphere, edges are assimilated by 10 11 the t of carbon dioxide a year also emits oxygen. Besides, various G. at volcanic eruptions which are allocated as a result of geochemical processes (sulfur dioxide gas, etc.), formed at bacterial decomposition of organic matters (methane and its homologs, carbon dioxide, hydrogen sulfide, nitrogen, oxygen, occasionally hydrogen and a large number of flying metabolites) are released into the atmosphere. The huge number of the most various G., including live organisms, dangerous to existence, gets to the atmosphere as a result of activity of the person in this connection more and more acute is a problem of pollution control of the environment (see).

In the industry more than 30 various G are used. They are applied in fuel quality, raw materials to the chemical industry, creation of an inert atmosphere during the welding and high-temperature processing of the nek-ry easily oxidized metals, as heat carriers and working bodies in internal combustion engines, in steam, jets, in gas turbines, in gas-discharge tubes, in special whistles for generation of ultrasonic fluctuations etc.

Constant exchange of G. between an organism and the environment surrounding it is one of the main living conditions of living beings (see. Gas exchange ).

A specific place is held by oxygen. This G., necessary for life activity, in big concentration and especially at supertension can lead to oxygen poisoning with euphoria at the first stages and with a loss of consciousness further. At a lack of oxygen there is air hunger (see. Hypoxia ). Oxygen found broad application in medical practice (see. Hyperbaric oxygenation , Oxygen therapy ).

Depending on their nature exert various impact on an organism. Carbon dioxide, ethylene, sulfur hexafluoride, xenon, nitrogen and argon (at supertensions), and also nitrous oxide and cyclopropane possess narcotic action (see. Drugs ). Two last G. found broad application in surgery for an inhalation anesthesia.

Possess Nek-rye G. to lay down. action and, being a part of mineral waters, to some extent cause them to lay down. properties (see. Mineralnye Vody ). Often mineral waters contain carbon dioxide, methane, hydrogen sulfide, radon and helium. Carbon dioxide is applied in balneotherapy (carbonic bathtubs). Fruit and mineral waters, champagne and nek-ry other drinks are saturated with carbon dioxide that impacts them a peculiar relish and the refreshing properties, and also increases firmness of drinks at storage.

The main (on volume) a component of respiratory mix — nitrogen — is in an organism in a small amount and only in the dissolved look. Free nitrogen in usual conditions, obviously, does not play any fiziol, roles, however at supertension (2 — 5 atm) can cause a caisson disease (see. Compressed-air disease ). For prevention of the last in respiratory mix for divers often use helium since it is very badly dissolved in blood. Use of helium is possible also in the atmosphere of cabins of spaceships.

Many G. constitute danger in the fire relation. Therefore G. used in life for simplification of their detection odorirut mercaptans, catches a smell to-rykh the person in insignificant concentration (3*10 - 1 g/cm 3 ). Many G. applied in the industry as raw materials or which are allocated at nek-ry productions are poisonous. Treat them: chlorine (see), fluorine (see), hydrogen chloride, hydrogen fluoride, carbon monoxide (see), etc. All gas dangerous productions are supplied with special devices — gas analyzers (see), watching concentration of harmful impurity in air. Careful observance of conditions of technical processes and the accident prevention sharply reduces number of cases acute or hron, poisonings with poisonous gases.


The table 1 TRANSITION TEMPERATURE of SOME SUBSTANCES FROM LIQUID STATE IN GASEOUS (And BACK)



the Table 2 &of KOHCTAHTnbsp VALUE; &anbsp; &inbsp; &bnbsp; FOR SOME GASES


the Note:       &anbsp;       — the constant, accounts howling forces of an attraction between molecules;   &bnbsp; — the constant considering the volume of particles.



Bibliography: Berkovich E. M. Energy balance is normal also of pathology, M., 1964, bibliogr.; Girshfelder Dzh., Curtice Ch. and Byrd River. The molecular theory of gases and liquids, the lane with English, M., 1961; Kikoin I. K. and Kikoin A. K. Molecular physics, M., 1963; Poling of L. The general chemistry, the lane with English, M., 1974; Pauling L. Molecular theory of general anesthesia, Science, v. 134, p. 15, 1961.

V. B. Akopyan.

Яндекс.Метрика