The kinetic theory of gases is a theoretical model that describes the molecular composition of the gas in terms of a large number of submicroscopic particles, which include atoms and molecules. Further, the theory explains that gas pressure arises due to particles colliding with each other and the walls of the container. The kinetic theory of gases also defines properties such as temperature, volume and pressure, as well as transport properties such as viscosity and thermal conductivity and mass diffusivity. It basically explains all the properties that are related to the microscopic phenomenon.
The significance of the theory is that it helps in developing a correlation between the macroscopic properties and the microscopic phenomenon. In simple terms, the kinetic theory of gases also helps us study the action of the molecules. Generally, the molecules of gases are always in motion, and they tend to collide with each other and the walls of the containers. In addition, the model also helps in understanding related phenomena, such as the Brownian motion.
Kinetic Theory of Gases Assumptions
The kinetic theory of gases considers the atoms or molecules of a gas as constantly moving point masses with huge inter-particle distances and may undergo perfectly elastic collisions.
Implications of these assumptions are as follows:
i) Particles
Gas is a collection of a large number of atoms or molecules.
ii) Point Masses
Atoms or molecules making up the gas are very small particles like a point (dot) on a paper with a small mass.
iii) Negligible Volume Particles
Particles are generally far apart such that their inter-particle distance is much larger than the particle size, and there is large free unoccupied space in the container. Compared to the volume of the container, the volume of the particle is negligible (zero volume).
iv) Nil Force of Interaction
Particles are independent. They do not have any (attractive or repulsive) interactions among themselves.
v) Particles in Motion
The particles are always in constant motion. Because of the lack of interactions and the free space available, the particles randomly move in all directions but in a straight line.
vi) Volume of Gas
Because of motion, gas particles occupy the total volume of the container, whether it is small or big, and hence the volume of the container is to be treated as the volume of the gases.
vi) Mean Free Path
This is the average distance a particle travels to meet another particle.
vii) Kinetic Energy of the Particle
Since the particles are always in motion, they have average kinetic energy proportional to the temperature of the gas.
viii) Constancy of Energy/Momentum
Moving particles may collide with other particles or containers. But the collisions are perfectly elastic. Collisions do not change the energy or momentum of the particle.
ix) Pressure of Gas
The collision of the particles on the walls of the container exerts a force on the walls of the container. Force per unit area is the pressure. The pressure of the gas is thus proportional to the number of particles colliding (frequency of collisions) in unit time per unit area on the wall of the container.
