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Introduction to Kinetic Theory of Gases

Thebehaviour of a gas in macroscopic terms can describe by using gaslaws suchas Boyle, Charles, and Gay-Lussac. These gas laws are based uponempirical observations. Atomic theory can also used to understand thebehaviour of a gas. According to atomic theory all substances arecomposed of a large number of very small particles called asmolecules or atoms. The observable properties of gas like pressure,volume, temperature are the consequence of the actions of theconstituent molecules of gas.


TheKinetic Theory of Gases Definition


The KineticMolecular Theory of Gases (KMT)is a batter option to understand the idealgas law, PV="nRT." This theory can used to describe the macroscopicproperties of a gas like pressure and temperature by using somepostulates. The five postulates of KineticMolecular Theory of Gases usedto describe the behaviour of molecules in a gas. According to KineticMolecular Theory Gases followgiven postulates;

  1. Gases are composed of small particles.These particles have a definite mass but no defined volume. Theytravel in straight line, have continuous random motion and obeyNewton's Laws.

  2. There is no intermolecular attractionsor repulsions force between gaseous particles. Therefore particlespossess no potential energy and their total energy equals to theirkinetic energies.

  3. Gaseous particles involve in elasticcollisions. Hence there is no net loss or gain of kinetic energywhen particles collide.

  4. The kinetic energy of gas is directlyproportional to the absolute temperature of the gas.

  5. The average kinetic energy is the samefor all gases at a given temperature can be given by;

K.E. = (1/2)mv2 =3kBT/2........(1)

Where; T=Absolute temperature

kB =Boltzmann constant (kB =1.381×10-23 m2 kgs-2 K-1)

Equation (1) states that the speed orvelocity of gas particles is related to their absolute temperature;therefore as temperature increases, speed of particles alsoincreases. The speed or velocity is directly proportional to kineticenergy.


The individual gas laws like Boyle law,Charle's law, and Gay-Lussac laws canbe connect with postulates of kinetic molecular theory of gases ;

  • As the number of collision betweenparticles increases, pressure of gas increases as pressure is forceper unit area which applies by gas particles due to theircollisions.

  • As volume of gas increases, the distancebetween particles increases.

  • The number of moles of particles is thenumber of particles of gas. As temperature of a gas is directlyrelated to the average speed of the particles. The statisticaldistribution of speeds of particles with temperature can berepresents by using given curve known as Maxwell distribution curve.