gas definition

It is a state of aggregation of matter in which the molecules are dispersed occupying the entire volume of the container that contains it, therefore, it does not have its own shape, a gas adapts the shape of the container container.

For example, one regularly hears about “natural gas” or “compressed air”; both are gases, the first is composed mainly of methane, while the second is a mixture of nitrogen, oxygen, noble gases, water and other gases that, due to the effect of pressure, is compressed.

The study of gases is very broad and interesting. It can be analyzed from the different scientists who studied their behavior, through the Laws that govern them to the differences between the ideal models and the observed reality.

Gases are described through a kinetic model that explains how the particles that form them move inside a container, always in a straight line colliding with the walls. Every time the particle bounces, it is considered that it does not lose kinetic energy and, therefore, its speed does not change, only its direction will change. So a gas with these characteristics, whose particles are in constant motion and never collide with each other, is considered an ideal gas.

pressure of a gas

When we want to study the compartment of gases we must define a fundamental term: pressure of a gas. Think of a bicycle tire (wheel), as we supply air with an inflator, the molecules of this gas hit the inner walls of the tire more and more frequently, acquiring greater firmness. Since pressure is a scalar magnitude that expresses the relationship between the force exerted in a certain area, each air particle exerts a certain pressure inside the tire since it is exerting a force on the walls. The most commonly used units of pressure are Pa, bar, atm, mm Hg and their derivatives.

Well, how do we relate the movements of the particles that form it with the pressure exerted? The greater the number of molecules inside, the greater the internal pressure on the walls that will allow the tire to stay inflated. Therefore, the pressure of a gas is proportional to the mass and the force with which the particles, in continuous movement according to the Kinetic Theory, hit the walls of the container. Such is the case of two soccer balls, the more deflated ball has less pressure because it has less mass inside.

We can ensure that most industries have compressed air supply as an auxiliary service current to their processes. How is compressed air generated? Use previously learned concepts. It is generated from a compressor, consisting of one or two pistons contained in a cylinder each. In one stage, the piston retracts to generate a pressure difference that allows air to enter the cylinder, and in a second stage, the piston advances “pushing” the air, applying pressure to it and consequently compressing it by reducing its volume. The compressed air is sent to a reservoir lung from where it will then be distributed in the different work stations.

This principle is also used by pressure gauges to measure the pressure inside a tire, for example. When we connect the needle at the inlet of the pressure gauge to the tire, this needle presses the tire valve also used for loading, when pushed and opened it allows the passage of air into the pressure gauge. Once the air enters the cylinder, it pushes the plunger by sliding it until the force of the air equals the force of the spring on the other side, which exerts a compression force. At this point, the pressure on the manometer is the pressure inside the tire and will be read on the graduated scale.

Temperature

The behavior of a gas is also closely related to the temperature to which it is exposed, since, if the temperature increases, the kinetic energy of the particles that form it increases, thus increasing collisions against the walls of the container and, therefore, As you can imagine, your pressure also increases. In this case, the volume remained constant, therefore the pressure increased, however, if the volume does not remain constant, the particles with greater kinetic energy will tend to occupy more space, so the volume will increase until the internal pressure equals the internal pressure. abroad.

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