We explain what the gaseous state is and the physical and chemical properties it presents. In addition, we explain its characteristics and examples.
What is the gaseous state?
The gaseous state is one of the states of aggregation of matter, along with the solid, liquid and plasma states. Matter in a gaseous state is called “gas”. It is characterized by being composed of its particles that are very loosely joined together.
Particles of substances in a gaseous state They have very little attractive force between themselves, so they expand throughout the length and width of the container in which they are located and adapt to its shape. This is because they vibrate with much greater energy and speed than in liquids or solids.
Because of this cohesion (forces that bind particles together) almost zero that gas particles have, they have an enormous capacity to be compressed. Compression is a process that is used industrially to liquefy gases, in this way they occupy a smaller volume and become easier to transport.
See also: Fire
Origin of the name gas
The term “gas” was coined by the Flemish-born scientist Jan Baptista van HelmontIn XVII century.
It comes from the Latin term chaos (“chaos”)since the observable state of the particles of a gas tends toward dispersion and apparent disorder.
Compared to solids and liquids, gas is the most chaotic state of matter.
Difference between gas and vapor
Vapor is a gas that, when compressed enough at a constant temperature, turns into a liquid. Gas, on the other hand, cannot be transformed into a liquid. in these conditions.
Physical properties of gases
Gases have the following physical properties:
- They do not have a defined shape, so they take the shape of the container in which they are contained.
- They do not have a defined volume, so they tend to take up the entire volume of the space where they are located.
- They are highly compressible, meaning that given the enormous space between their particles, they can be forced to occupy a smaller volume.
- Gases are fluids, like liquids, and can move with little friction from one container to another.
- The gas particles are so far apart that their total weight is less and they are less affected by gravity, so they can remain suspended in the atmosphere.
- Gases can be more or less dense than air (depending on their nature), that is, they can rise or fall once they are released into the atmosphere.
- The taste, smell and color of gases depends on the chemical elements that compose them.
- Gases diffuse rapidly in a vacuum or between other gases.
Chemical properties of gases
The atoms and molecules of a gas are far apart from each other. and moving at very high energy levels. This makes it impossible for them to remain together and rigid as in the case of solids.
The state of aggregation of matter does not alter the chemical properties of the substances that compose it. Therefore, the chemical nature of gases can vary enormously: some They may be inert, others flammable, corrosive or toxicdepending on the chemical reactivity of its elements.
General gas law
The general gas law describes the general behavior of gases, combining a set of more specific laws such as the Boyle-Mariotte Law, the Charles Law and the Gay-Lussac Law. All of them refer to the behavior of pressure, volume and temperature of gases.
In all the previous equations V1, P1 and T1 They are the volume, pressure and initial temperature. While V2, P2 and T2 are the volume, pressure and final temperature.
The General Gas Law proposes that, combining the previous laws, we have:
Here, Q It is the pressure, V is the volume, T is the temperature and c It is a constant.
Ideal gases
Ideal gases are called hypothetical or theoretical gases that are a man-made model of gases to study and explain the behavior of gases in a simpler way. To study this type of gases, the equation of state of ideal gases can be used, which is represented as:
Where Q It’s the pressure V is the volume, T is the temperature, n the number of moles of gas (which must remain constant) and R the ideal gas constant (equal to 8.314472 J/molK).
The properties of ideal gases are:
- They are made up of a certain number of molecules.
- There are no forces of attraction or repulsion between its molecules.
- There is no collapse between the molecules, nor changes in their physical nature (i.e., phase changes).
- An ideal gas always occupies the same volume, under the same conditions of pressure and temperature.
More on: Ideal gases
Real gases
Real gases are those that exist in real life. The behavior of these gases cannot be studied using the ideal gas equation of state, but rather Its study requires the use of more complex equationsIn real gases, unlike ideal gases, the interactions between their particles must be taken into account. In addition, phase transitions may occur in these gases.
Changes of state in gases
- Evaporation. Also called “vaporization” is the process in which a liquid turns into a gaseous state. This process occurs daily, when the heat energy of liquids increases, for example, due to sunlight or when they are heated. Evaporation occurs gradually and it is not necessary for the entire liquid to be heated to its boiling point (temperature at which the vapor pressure of the liquid becomes equal to the pressure surrounding the liquid), it is sufficient for it to be heated to let it evaporate little by little.
- BoilingIt is the process by which, when the temperature of a liquid increases above its boiling point, it transforms into a gas. For this to occur, the entire mass of the liquid must be heated to a temperature equal to or greater than the boiling point.
- SublimationIt is the phase change process that goes from the solid state to the gaseous state, without first passing through the liquid state. Although under certain conditions of pressure and temperature it can occur with ice, it occurs more frequently with other substances, such as iodine, which at 184 ºC goes directly from the solid to the gaseous state.
- Reverse sublimation. Also called deposition, this phase change is contrary to sublimation, that is, it involves the passage from gaseous directly to solid, without first passing through the liquid state. It takes place under very specific pressure conditions, which force the gas particles to come together to form rigid molecular structures. A common example of reverse sublimation occurs at the Earth’s poles, on mountain peaks, or in any other environment where the temperature is so low that liquid water is not formed from moisture, but rather ice and snow.
- Condensation. It is the opposite process to evaporation, it involves the subtraction of heat energy from a gas. As a result, its particles move more slowly and come together more easily, and become liquid droplets on surfaces or precipitate to the ground. This is what happens in the lower atmosphere when, after moving away from the Earth’s surface, the evaporated water vapour cools and forms clouds, from which the water droplets fall back to the ground: that is rain. It can also occur when ambient humidity (gaseous state) comes into contact with a cold surface, such as a bottle.
Examples of compounds in the gaseous state
Some examples of matter in a gaseous state are:
- Water steamWhen water evaporates, it changes to a gaseous state in the form of steam: something that is perfectly evident when we boil water and a column of whitish steam emerges from the pot.
- Air. The air we breathe is a homogeneous mass of gas, a mixture of very different elements such as oxygen (O2), hydrogen (H2) and nitrogen (N2), which are generally transparent, colorless and odorless.
- ButaneIt is an organic gas derived from petroleum, composed of flammable hydrocarbons. It is commonly used as fuel to generate fires in our kitchens, when we open the tap and this gas emerges.
- Methane. It is another hydrocarbon gas, a frequent byproduct of the decomposition processes of organic matter. It is possible to find it in swamps, sewers or even in the intestines of animals, where there are anaerobic bacteria that produce it. It has a very characteristic unpleasant odor.