9 junio, 2024

Gaseous state: characteristics, general law, examples

He gaseous state It is a state of aggregation of matter in which the particles are held together by weak interactions, being able to move in all directions of the container that contains them. Of all the physical states of matter, the gaseous state is the one that manifests the greatest freedom and chaos.

Gases exert pressure, carry heat, and are made up of all sorts of small particles. Our atmosphere and the air we breathe is a manifestation of the gaseous state here on Earth.

Examples of gases are greenhouse gases, such as water vapor, carbon dioxide, methane or ozone. The carbon dioxide that we exhale in our breath is another example of a gaseous substance.

Liquids and solids, for example, will not move to positions beyond their own material limits, a fact that gases do not. The smoke from cigarettes, chimneys and towers demonstrate by themselves how the gas is rising and dispersing through the environment without anything stopping it.

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Characteristics of the gaseous state

Lacks volume or shape

The gaseous state is characterized by not having a defined shape or volume. If there are no borders to hold it back, it will disperse throughout the atmosphere. Even as with helium, it will escape outside of Earth.

A gas can only acquire the form imposed by a container. If a container is cylindrical, the gas will «have» the shape of a cylinder.

poor conductor of heat

This state is also characterized by being a poor conductor of both heat and electricity. It is generally less dense compared to the solid and liquid states.

Since most gases are colorless, such as oxygen and carbon dioxide, you can determine how much of them are in a container by measuring its pressure.

reagents

Gases tend to be more reactive, with the exception of noble gases, than liquids or solids, so they are potentially dangerous, either due to fire hazards, or because they can easily enter the respiratory systems of individuals.

small particles

Gaseous particles are also usually small, being simple atoms or molecules.

For example, gaseous hydrogen, H2, is a very small molecule made up of two hydrogen atoms. Likewise, we have helium, He, whose atoms are even smaller.

interactions

The interactions in the gaseous state are negligible. In this it differs enormously from the liquid and solid states, in which its particles are highly cohesive and strongly interact with each other. In the molecules that form the liquid and solid states there is hardly any molecular vacuum between them.

The particles in the gaseous state are very far apart from each other, there is a lot of vacuum between them. It is no longer a vacuum on a molecular scale. The distance that separates them is so great that each particle in the gas is free, indifferent to its surroundings, unless it collides with another particle or against the wall of the container in its chaotic trajectory.

Assuming there is no container, the void between the gas particles can be filled by air, which pushes and drags the gas in the direction of its flow. That is why air, which consists of a gaseous mixture, is capable of deforming and spreading gaseous substances through the sky, as long as they are not much denser than it.

General law of the gaseous state

The experimental study of the behavior and mechanics of gases led to several laws (Boyle, Charles, Gay-Lussac) that combine to be able to predict what the parameters of any gaseous system or phenomenon will be, that is, what will be its temperature, volume and pressure.

This general law has the following mathematical expression:

P = KT/V

where K is a constant, P is the pressure, V is the volume, and T is the temperature of the gas in kelvin scale. Thus, knowing two variables (namely, P and V), the third can be cleared, which would become the unknown (T).

This law makes it possible to know, for example, what the temperature of a gas, enclosed in a container of volume V, must be in order to exhibit a pressure P.

If we add the contribution of Amadeus Avogadro to this law, we will then have the ideal gas law, which also involves the number of particles, and with them the molar concentration of the gas:

P = nRT/V

Where no corresponds to the number of moles of the gas. The equation can be rewritten as:

P = cRT

Where c is the molar concentration of the gas (no/V). Thus, from a general law, the ideal law is obtained that describes how the pressure, concentration, temperature and volume of an ideal gas are related.

Examples of gaseous state

gaseous elements

The same periodic table offers a good repertoire of examples of elements that occur on Earth as gases. Between them we have:

-Hydrogen

-Helium

-Nitrogen

-Oxygen

-Fluorine

-Chlorine

-Neon

-Argon

-Krypton

-Xenon

This does not mean that the other elements cannot become gaseous. For example, metals can turn into gases if they are subjected to temperatures higher than their respective boiling points. Thus, there may be gases from particles of iron, mercury, silver, gold, copper, zirconium, iridium, osmium; of any metal.

gaseous compounds

In the following list we have some examples of gaseous compounds:

-Carbon monoxide, CO

-Carbon dioxide, CO2 (gas that makes up our exhalations)

-Ammonia, NH3 (vital substance for industrial process augers)

-Sulfur trioxide, SO3

-Methane, CH4 (domestic gas, with which you cook)

-Ethane, CH3CH3

-Nitrogen dioxide, NO2 (brown colored gas)

-Phosgene, COCl2 (highly poisonous substance)

-Air (being a mixture of nitrogen, oxygen, argon and other gases)

-Water vapor, H2O (which is part of clouds, geysers, machine vaporizers, etc.).

-Acetylene, HC≡CH

-Iodine vapors, I2 (purple colored gas)

-Sulfur hexafluoride, SF6 (very dense and heavy gas)

-Hydrazine, N2H4

-Hydrogen chloride, HCl (which dissolved in water produces hydrochloric acid)

References

Whitten, Davis, Peck & Stanley. (2008). Chemistry. (8th ed.). CENGAGE Learning.
Wikipedia. (2020). Gas. Retrieved from: en.wikipedia.org
Edward A. Mason. (February 6, 2020). Gas. Encyclopædia Britannica. Recovered from: britannica.com
Helmenstine, Anne Marie, Ph.D. (February 11, 2020). Gas Definition and Examples in Chemistry. Retrieved from: thoughtco.com
Maria Estela Raffino. (February 12, 2020). What is the gaseous state? Retrieved from: concept.de

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