August 19, 2022

The gaseous state in physics and in chemistry is one of three states that are interested in thermodynamics, beside the liquid state and the solid state. Gases are fluids, meaning that they have the ability to flow and do not resist changing their shape, although they have a viscosity. Unlike what happens in liquids, gases are free and do not occupy a fixed volume, but they fill any space available to them. kinetic energy Gases are the second most important thing in states of matter (after plasma). Due to the increase in the kinetic energy of gases, the gas molecules and atoms tend to occupy every available volume, but also permeate through a barrier of porous material, and this increases by increasing its kinetic energy. There is a misconception that the collision of particles with each other is necessary to determine the pressure of the gas, but the fact is that their random velocities are sufficient to determine its pressure. Collisions between molecules are only important for chemical reactions where the collision theory explains the interaction of molecules between two substances. The Maxwell-Boltzmann distribution also describes the distribution of velocities of molecules in a gas and their dependence on temperature and takes into account the thermal motion of the gas. The motion of gas particles is different from the motion of fluid particles in contact. When particles, such as grains of dust in a gas, are present, we find that they move in a Brownian motion, and we sometimes see this in the sun's rays and the movement of dust in the air. Since there is no current technology that enables us to observe the movement of a gaseous particle (an atom or a molecule), the theoretical calculations only give an idea of ​​how they move, but the movement of atoms of a gas or a gas consisting of molecules (oxygen) or nitrogen, where each consists of two bonded atoms, It is different from the Brownian movement. The reason for this is that Brownian motion includes the motion of a dust particle under the influence of the resultant collision of gas atoms with it. Dust particles are often made up of billions of atoms. And it moves in sharp shapes at random.

Theory of thermal motion of gases

The development of thermal motion and the understanding of gases and their behavior motivated the progress of chemistry and physics since Robert Boyle's discoveries and his formulation of their behavior in Boyle's Law in 1662. Then there was rapid progress until the nineteenth century, and scientists were able to describe the gas as follows: Gases consist of large numbers of tiny particles that are far from each other for their size. As a result, most of the volume occupied by the gas is a vacuum, and this explains the low density of gases. Gas particles collide with each other due to their fast, random movement. As the temperature increases, the velocities of the particles increase, the collisions intensify, and the rate of collisions increases. At the same time, gas particles hit the wall of the container that contains them and appear to us in the form of pressure. ‎