Gases are understood as all substances that are in this state of matter aggregation, that is, substances whose molecules interact weakly, when they are under specific pressure and temperature circumstances, without molecular bonds being formed, having weak interactions, so these substances take the shape of the container that contains them, having the tendency to expand as a result of their high kinetic energy.
They are substances that, because they have large empty spaces between each molecule, have a high capacity to be compressed, being that being “free” molecules, they can be perfectly distributed in the container or place that contains them, adopting the shape of this, by not have a definite shape.
Gases can be classified according to various criteria, for their chemical composition, for belonging to the group of noble gases, for the use they are given, for their toxicity, etc.
Main types of gases:
Noble or inert gases.- They are called noble or inert gases, those that have low reactivity and are chemical elements, which have some characteristics similar to each other. Under normal conditions, they are monatomic, colorless, and odorless. These are argon (Ar), helium (He), neon (Ne), radon (Rn), krypton (Kr) and xenon (Xe), which are found at the far right of the periodic table of the chemical elements.
Combustible gases.- These are those that can be used as fuel thanks to the fact that energy can be produced by using them by “burning” them, since they allow the release of energy when they are subjected to a stimulus (turn them on). They burn easily in the presence of oxygen that is present in the air or in the presence of another oxidant. This is the case, for example, of methane gases and those that are extracted from hydrocarbons, such as natural gas and liquefied petroleum gas, as well as hydrogen, or helium 3 (an isotope of helium that can be used as fuel) , among others.
Corrosive gases.- They are those gases or gaseous substances that contribute to corrosion to varying degrees, an example is oxygen that corrodes iron, likewise there are several gases and mixtures in a gaseous state, which have variable corrosive effects, both in metals or as in other bodies, it is the case of gaseous substances such as gaseous chlorine, nitrogen monoxide, ethylene oxide, nitrogen dioxide and others. It is as a consequence of the corrosion that they have, which can be harmful to health, damaging organic tissues.
Toxic gases.- In addition to the aforementioned corrosive gases, there are others that cause damage to living organisms, these are gases or compounds in a gaseous state, which are toxic to the body, either due to high corrosion or because they have poisonous effects. in the body when inhaled.
Some of them have been used during wars precisely because of their lethal effects, especially in the case of gases that are not found in nature, but are chemical combinations created by man, for use as pesticides or directly as weapons, as is the case of mustard gas and nerve gas, (such as sarin), being substances that are released in the form of gas and affect the human (and animal) organism, causing irreparable damage and/or death.
Other toxic gases are of natural origin, such as the gases expelled by volcanoes when they erupt, such as sulfur dioxide, as well as gases that are formed after the chemical reactions of some elements and substances, such as chemical reactions with the metal cyanide resulting from them a toxic and lethal gas (cyanide gas).
Oxidizing gases.- At first the term oxidation (of oxygen) was given to the reaction that occurs to metals in the presence of oxygen, however, as there are similar reactions with other gases, such as chlorine in the form gas, which produces a similar effect on iron, this type of reaction is called indistinctly oxidation. The best known oxidizing gas is oxygen, with some others such as chlorine and fluorine gases (which are substances that occur at room temperature in gas form).
Liquefied.- These are those gases that are subjected to the “liquefied” process, that is, they are those that have been subjected to a process that transforms them from the gaseous to the liquid state, through processes of decreasing temperature and increasing the pressure, which results in the condensation of the molecules. This process is common in hydrocarbon gases, for their better storage, transport and use, for example in gas lighters, tanks or in underground distribution systems.
Cryogenic.- This is the name given to liquefied gases, which become liquid at extremely low temperatures, and which are characterized by an extremely high speed, to go from the liquid to the gaseous state, so their handling must be carried out with Be careful because they are dangerous. Examples of them are oxygen, hydrogen and nitrogen, which can only be liquefied at very low temperatures.