Gas

In addition to solid and liquid is gaseous one of the three classical states of matter. A substance is then a gas when the particles move at a great distance from each other freely and fill the available space evenly. Compared to solid or liquid takes the same mass as a gas under normal conditions the around one thousand to two thousand times the space.

Together with the gases to the liquids are fluids.

Etymology

The origin of the word gas was unclear for a long time. Although more or less known that the word as a technical term in the 17th century by the Belgian physician and naturalist Johan Baptista van Helmont († 1644) was introduced on the etymology, however, were uncertain, and it was origin, inter alia, from the Hebrew, from Dutch. geest ( "spirit" ), from Dutch. synergists ( " ferment " ) or German gäsen ( Paracelsus for " ferment " ), gäscht ( " foam " on fermenting liquid) suspected. The clarification was in 1859 brought about by the linguist Matthias de Vries, a statement from van Helmont's Ortus Medicinae (Amsterdam 1648) taught what this word specifically for the damage by cold mist of water re-created consciously and here an allusion to the Greek, in Dutch had very similar aims χάος spoken word ( "chaos" ): " ideo paradoxi licentia, egestate in nominis, halitum illum gas vocavi, non longe a chao veterum secretum " ( "In the absence of a name I have taken the liberty to unusual, to call this breath gas because he is from the chaos of the ancients little different. ").

The aggregate state gaseous

The physical state "gaseous" is created from the " solid " or " liquid " form of energy ( heat). Already sufficient for some elements and compounds the standard conditions (temperature 20 ° C, pressure 1 bar) to be present as a gas; at sufficiently high temperatures, however, any material is put into the gaseous state. Thereby the energy supplied to the kinetic energy of the individual particles ( depending on the temperature at speeds in the range of 1000 m / s), which causes the gaseous state with the complete filling of the space with predetermined statistical equal distribution of the gas. Here, the overall system seeks the state of highest entropy of (second law of thermodynamics ). That this is the most likely state, one can make the following manner clearly: you Divides mentally the gas volume available in space cells of about the size of a molecule, then there are many more ways that molecules on the many cells of the whole volume distribute as a small fraction. The macrostate of the distribution, the most bulky configuration options ( micro-states ) of the particles and therefore also the highest entropy. The number of micro-states, the statistical weight can be calculated. More details at entropy ( thermodynamics) / examples.

Properties

For ideal gases the free mobility of individual particles according to the kinetic theory of gases is perfect; this condition is only at high temperatures above the boiling point is reached ( which is the case for hydrogen and helium even at room temperature).

If you fill any ideal gas in a given volume, so always located at the same pressure and temperature is the same number of particles (atoms or molecules) that is independent of the mass of each particle and thus independent of the type of gas. In quantitative claimed under normal conditions, one mole (that's according to Avogadro 6.022 × 1023 particles ) of any gas a space of 22.4 liters ( see also Molar volume and Avogadro 's constant ).

For real gases more or less great attractions of the particles are mutually effective ( van der Waals forces ). The difference is noticeable when compressing: gases are compressible, the volume of an ideal gas is inversely proportional to the pressure ( state equation). Real gases deviate from the principles described above from more or less.

Gases also exhibit properties of fluids: flow and resist deformations not, although they are viscous.

State transitions

The transition from the liquid to the gaseous state is referred to as evaporation ( above boiling point ), or evaporation ( below the boiling point ), the reverse transition from the gaseous to the liquid state of condensation. The direct transition from the solid to the gaseous state is the sublimation, the reverse transition from the gaseous to the solid state is called Resublimation.

Storage

To store a largest possible amount of gas in a container, that is to obtain a high density, the gas is highly compressed (see also compressed gas ). For the purpose of high- pressure load capacity of the gas container usually cylindrical or spherical pressure tanks can be used (e.g., gas cylinders ). Gas boiler or Gasometer are low-pressure storage with large geometric volume. Due to the low pressure ( < 1 bar) is the stored quantity but insignificant. Gas supplier store the gas usually in the line network ( gas grid ) by using high- pressure pipes with large diameter.

Related Topics

  • Indication of the purity of material with technical gases
  • Steam is a historically older term to refer to a substance in the gaseous state of matter that exists as a liquid under normal conditions ( see, eg, water vapor).
  • Vapor formation due to cavitation
  • Electron gas
  • Natural gas ( energy and economic factor )
  • LPG
  • Ideal Fermi gas
  • Gas transport
  • Linde process for the liquefaction of gases
  • Detection of gases
  • Physical properties of gases, see Gas Laws
  • Special kinds of gases and gas mixtures, see Category: Gas
  • City ​​Gas
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