GASES: PROPERTIES, BEHAVIOR, SHAPE, EXAMPLES - CHEMISTRY - 2025

The gases are all those substances or compounds whose aggregation states are weak and scattered, while highly dependent on temperature and pressure conditions governing over them. They are perhaps the second most abundant form of matter in the entire Universe after plasma.

On Earth, gases make up the layers of the atmosphere, from the exosphere to the troposphere and the air we breathe. Although a gas is invisible when it is diffused through large spaces, such as the sky, it is detected by the movement of clouds, the turns of the blades of a mill, or by the vapors exhaled from our mouths in cold climates.

The gases can be observed in industrial or home chimneys, as well as in the smoke towers emanating from volcanoes. Source: Pxhere.

Likewise, going to the negative environmental aspects, it is observed in the black smoke from the exhaust pipes of the vehicles, in the smoke columns of the towers located in the factories, or in the smoke raised when a forest burns.

You are also faced with gaseous phenomena when you see vapors that come out of the sewers, in the wisps of swamps and cemeteries, in the bubbling inside the fish tanks, in the helium balloons that are released into the sky, in the oxygen released by plants as a result of their photosynthesis, and even in belching and flatulence.

Wherever gases are observed means that there was a chemical reaction, unless they are fixed or assimilated directly from the air, the main source of gases (superficially) on the planet. As temperatures rise, all substances (chemical elements) will transform into gases, including metals such as iron, gold, and silver.

Regardless of the chemical nature of gases, they all share in common the great distance that separates their particles (atoms, molecules, ions, etc.), which move chaotically and arbitrarily through a given volume or space.

Properties of gases

Differences in solid, liquid and gas molecules

Physical

The physical properties of gases vary depending on what substance or compound is involved. Gases are popularly associated with bad odors or putrefaction, either due to their sulfur content, or to the presence of volatile amines. Likewise, they are visualized with greenish, brown or yellowish colorations, which intimidate and give a bad omen.

However, most gases, or at least the most abundant, are actually colorless and odorless. Although they are elusive, they can be felt on the skin and they resist movement, even creating viscous layers in the bodies that pass through them (as happens with airplanes).

All gases can experience changes in pressure or temperature that end up turning them into their respective liquids; that is, they suffer condensation (if cooled) or liquefaction (if “pressed”).

Condensation; from gaseous state to liquid state

On the other hand, gases are capable of dissolving in liquids and some porous solids (such as activated carbon). Bubbles are the result of accumulations of gases that have not yet dissolved in the medium and escape to the surface of the liquid.

Electrical and thermal conductivity

Under normal conditions (without ionization of their particles), gases are poor conductors of heat and electricity. However, when stressed with many electrons, they allow current to pass through them, as seen in lightning during storms.

On the other hand, at low pressures and subjected to an electric field, some gases, especially the noble or perfect ones, light up and their lights are used for the design of advertisements and night posters (neon light), as well as in the famous electric discharge lamps in street lanterns.

Regarding thermal conductivity, many gases behave as thermal insulators, so their incorporation in the filling of fibers, fabrics, or glass panels, helps prevent heat from passing through them and keeps the temperature constant.

However, there are gases that are good conductors of heat, and can cause worse burns than those caused by liquids or solids; for example, as it happens with the hot steam of the baked cupcakes (or empanadas), or with the steam jets that escape from the boilers.

Reactivity

Generally, reactions that involve gases, or where they occur, are classified as dangerous and cumbersome.

Their reactivity depends, again, on their chemical nature; However, when expanding and moving with great ease, greater care and control must be exercised because they can trigger drastic increases in pressure that put the reactor structure at risk; This is not to mention how flammable or non-flammable these gases are.

Behavior of gases

Macroscopically one can get an idea of ​​the behavior of gases by witnessing how smoke, rings, or the literary "tongues" of cigarettes evolve in the air. Likewise, when a smoke grenade explodes, it is interesting to detail the movement of these different colored clouds.

However, such observations are subject to the action of air, and also to the fact that there are very fine solid particles suspended in the smoke. Therefore, these examples are not enough to reach a conclusion regarding the true behavior of a gas. Instead, experiments have been conducted and the kinetic theory of gases developed.

Molecularly and ideally, gaseous particles elastically collide with each other, having linear, rotational and vibrational displacements. They have an associated average energy, which allows them to travel freely through any space without almost interacting or colliding with another particle as the volume around them increases.

Its behavior would come to be a mixture of the erratic Brownian movement, and that of some collisions of some billiard balls that bounce incessantly between each other and the walls of the table; if there are no walls, they will diffuse into infinity, unless they are held back by a force: gravity.

Form of gases

Gases, unlike liquids and solids, are not matter of the condensed type; that is, the aggregation or cohesion of its particles never manages to define a shape. They share with liquids the fact that they completely occupy the volume of the container that contains them; however, they lack surface and surface tension.

If the gas concentration is high, its "tongues" or the macroscopic forms already described can be seen with the naked eye. These, sooner or later, will end up vanishing due to the action of the wind or the mere expansion of the gas. The gases therefore cover all the corners of the limited space originating highly homogeneous systems.

Now, the theory conveniently considers gases as spheres that hardly collide with themselves; but when they do, they rebound elastically.

These spheres are widely separated from each other, so the gases are practically "full" of vacuum; hence its versatility to pass through the slightest slit or fissure, and the ease of being able to significantly compress them.

That is why, no matter how closed a bakery installation is, if you walk next door it is sure that you will enjoy the aroma of freshly baked bread.

Pressure of a gas

It could be believed that because the spheres or particles of the gas are so dispersed and separated, they are incapable of generating any pressure on the bodies or objects. However, the atmosphere proves that such a belief is false: it has mass, weight, and prevents liquids from evaporating or boiling out of nowhere. Boiling points are measured at atmospheric pressure.

Gas pressures become more quantifiable if manometers are available, or if they are enclosed in containers with non-deformable walls. Thus, the more gas particles there are inside the container, the greater the number of collisions between them and its walls.

These particles, when they collide with the walls, press them, since they exert a force proportional to their kinetic energy on their surface. It is as if the ideal billiard balls were thrown at a wall; if there are many that hit them at high speed, it could even break.

Units

There are many units that accompany measurements of the pressure of a gas. Some of the best known are millimeters of mercury (mmHg), like torr. There are those of the international system of units (SI) that define the pascal (Pa) in terms of N / m ²; and from him, the kilo (kPa), mega (MPa) and giga (GPa) pascal.

Volume of a gas

A gas occupies and expands throughout the volume of the container. The bigger the container, the volume of the gas will be too; but both its pressure and density will decrease for the same amount of particles.

The gas itself, on the other hand, does have an associated volume that depends not so much on its nature or molecular structure (ideally), but on the pressure and temperature conditions that govern over it; this is, its molar volume.

In reality, the molar volume varies from one gas to another, although the variations are small if they are not large and heterogeneous molecules. For example, the molar volume of ammonia (NH ₃, 22.079 L / mol) at 0 ° C and 1 atm, differs from that of helium (He, 22.435 L / mol).

All gases have a molar volume that changes as a function of P and T, and no matter how large their particles are, the number of them is always the same. Hence in fact it derived by what is known Avogadro's number (N _A).

Main gas laws

The behavior of gases has been studied for centuries through experiments, in-depth observations, and interpretation of the results.

Such experiments made it possible to establish a series of laws that, put together in the same equation (that of ideal gases), help to predict the responses of a gas to different conditions of pressure and temperature. In this way, there is a relationship between its volume, temperature and pressure, as well as the number of its moles in a given system.

Among these laws are the following four: Boyle, Charles, Gay-Lussac and Avogadro.

Boyle's Law

Increase in pressure by reducing the volume of the container. Source: Gabriel Bolívar

Boyle's law states that at constant temperature, the volume of an ideal gas is inversely proportional to its pressure; that is, the larger the container, the lower the pressure that its walls will experience from the same amount of gas.

Charles Law

Chinese lanterns or wish balloons. Source: Pxhere.

Charles's law states that at constant pressure, the volume of an ideal gas is directly proportional to its temperature. Balloons demonstrate Charles's law, because if they are heated they inflate a little more, while if they are submerged in liquid nitrogen, they deflate because the volume of the gas inside them contracts.

Gay-Lussac Law

Gay-Lussac's law states that at constant volume, the pressure of an ideal gas is directly proportional to its temperature. In a well-closed cauldron, if a gas is heated progressively, each time the pressure inside it will be greater, because the walls of the cauldron do not deform or expand; that is, its volume does not change, it is constant.

Avogadro's Law

Finally, Avogadro's law states that the volume occupied by an ideal gas is directly proportional to the number of its particles. Thus, if we have one mole of particles (6.02 · 10 ²³), then we will have the molar volume of the gas.

Types of gases

Combustible gases

They are those gases whose components function as fuels, because they are used for the production of thermal energy. Some of them are natural gas, liquefied petroleum gas, and hydrogen.

Industrial gases

They are those manufactured gases, which are marketed to the public for different uses and applications, such as for the health, food, environmental protection, metallurgy, chemical industry, security sectors, among others. Some of these gases are oxygen, nitrogen, helium, chlorine, hydrogen, carbon monoxide, propane, methane, nitrous oxide, among others.

Inert gases

They are those gases that under specific temperature and pressure conditions, do not generate any chemical reaction or a very low one. They are neon, argon, helium, krypton, and xenon. They are used in chemical processes in which non-reactive elements are necessary.

Examples of gaseous elements and compounds

What are the gaseous elements of the periodic table under Earth conditions?

We first have hydrogen (H), which forms H ₂ molecules. Helium (He), the lightest noble gas, follows; and then nitrogen (N), oxygen (O) and fluorine (F). These last three also form diatomic molecules: N ₂, O _2, and F ₂.

After fluorine comes neon (Ne), the noble gas that follows helium. Below fluorine we have chlorine (Cl), in the form of Cl ₂ molecules.

Next we have the rest of the noble gases: argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) and oganeson (Og).

Therefore, they are a total of twelve gaseous elements; eleven if we exclude the highly radioactive and unstable oganeson.

Gaseous compounds

In addition to gaseous elements, some common gaseous compounds will be listed:

-H ₂ S, hydrogen sulfide, responsible for the smell of rotten eggs

-NH ₃, ammonia, that pungent aroma that is perceived in used soaps

-CO ₂, carbon dioxide, a greenhouse gas

-NO ₂, nitrogen dioxide

-NO, nitrogen monoxide, a gas that was believed to be highly toxic but plays an important role in the circulatory system

-SO ₃, sulfur trioxide

-C ₄ H ₁₀, butane

-HCl, hydrogen chloride

-O ₃, ozone

-SF ₆, sulfur hexafluoride

References

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