We explain what gases are, how they are classified and the properties they have. We also explain their characteristics and examples.
What are gases?
By the term gas we refer to one of the three main states of aggregation of matter (along with liquids and solids). It is characterized by dispersion, fluidity and low attraction between its constituent particles.
Gases are the most volatile form of matter in nature and they are extremely common in everyday life. Thus, when a substance is in a gaseous state we usually call it a gas.
Liquid or solid substances can be transformed into gas using different processes. This transformation involves a change in the physical properties of the substances, such as their state of aggregation. However, their chemical properties do not change, since the substances continue to have the same chemical structure, that is, chemical bonds do not break and new substances are not generated.
The gases They are found everywhere: from the heterogeneous mass of gases that we call the atmosphere and that we breathe as air, to the gases generated inside the intestine, the product of digestion and decomposition, to the flammable gases that we use to feed our kitchens and ovens.
See also: Aggregation states
History of gases
The word gas It was invented in the 17th century by the Flemish scientist Jan Baptista van Helmontfrom the Latin term chaos (“chaos”).
He chose the name because of the apparent degree of disorder exhibited by the molecules of a gas. Also This state was known as the “aeriform state.”but this term fell into disuse.
The first laws on the behavior of gases were a consequence of their intensive study at the end of the same century, especially of their relationships between pressure, temperature and volume.
This led to Émile Clapeyron to formulate the ideal law for all gases (“Ideal Gas Law”) in 1834.
Ideal gas and real gas
An ideal gas is a gas model created by humans., and that it has no interactions between the particles that form it, that is, they have no attraction or repulsion between them. On the other hand, a real gas does present these interactions.
The simpler the chemical formula of a real gas and the lower its reactivity, the more it can resemble an ideal one. Thus, monatomic gases, for example, helium (He), are those that behave most similarly to ideal gases.
More in: Ideal gases
Gas laws
One of the most used laws to describe the behavior of gases is the Ideal Gas Law which, in turn, can be understood as the combination of other laws:
Types of gases
Gases can be classified according to their chemical nature into:
- Combustible or flammable. Those that can burn, that is, generate explosive or exothermic reactions in the presence of oxygen or other oxidants.
- Corrosives. Those that, when coming into contact with other substances, subject them to intense reduction or oxidation processes, generating damage to their surface or wounds in the case of organic matter.
- Oxidizing agents. Those that allow a flame or a flammable reaction to remain alive, since they induce combustion in other substances.
- ToxicThose that represent a danger to health due to the reactions they introduce into the body of living beings, such as radioactive gases.
- Inert or noble. Those that present little or no reactivity, except in certain situations and conditions.
Properties of gases
Gases have the following properties:
- They do not have their own volume. They occupy the volume of the container in which they are located.
- They have no form of their own. They also assume that of their container.
- They can expand and contract. Like solids and liquids, gases expand if their temperature is increased, and contract if they cool.
- They have great fluidityGases flow much more than liquids because their particles have less interaction. They can easily move through an orifice from one container to another.
- They have high diffusionGases can easily mix with each other due to the great movement of their particles.
- Solubility. Gases can be soluble in water or other liquids.
- They can be compressedBy applying pressure to a gas, its particles can be brought closer together, that is, the gas is compressed.
Changes of state of gases
- Sublimation. It is a physical process of phase change, which allows a solid to be converted directly into a gas, without first going through a liquid stage. This process is rare and usually involves specific pressure and temperature conditions. We can observe it in dry ice (or ice) at room temperature: the solid block gives off a slight vapor which is the substance recovering its original gaseous state.
- Boiling. It is the process by which a liquid transforms into a gas. It occurs when the entire mass of the liquid is heated to a temperature equal to its boiling point.
- EvaporationIt is an extremely common phase change process, which leads a liquid to become a gas when the temperature of the liquid is increased. It occurs slowly and gradually. We put it into practice, for example, in the shower when very hot water turns into vapor that can be seen as a whitish cloud.
- CondensationIt is the opposite process to evaporation, that is, a phase change process that leads from the gaseous state to the liquid, due to the loss of heat energy. This lost energy causes the gas particles to vibrate more slowly, allowing them to approach and interact more closely, as occurs on cold glass on a rainy day, or on plants and other surfaces with dew.
- Reverse sublimationIt is the opposite of sublimation, that is, the transition from the gaseous state to the solid state without first going through a moment of liquidity. This process requires very specific pressure and temperature conditions.
Plasma
The plasma state of matter It is considered a fourth state of aggregationbut it has enormous similarities with the gaseous state, since it is basically an ionized gas, that is, a gas whose particles have lost electrons and have acquired a certain electromagnetic charge. There are cold plasmas, such as those used in “lava” lamps, or hot plasmas, such as the fire that surrounds the Sun.
Examples of gases
Some examples of gases are:
- Hydrogen (H2). It is the most common diatomic gas in the entire universe.
- Helium (He)Tasteless, colorless and inert, it is the least soluble in water of all gases.
- Methane (CH4). It is a gaseous hydrocarbon with an unpleasant odor that is obtained as a product of the decomposition of organic matter.
- AirIt is the heterogeneous mixture of hydrogen, nitrogen, oxygen, argon and other gases that living beings breathe.
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