KINETIC GAS THEORY - postulate, limitation of kinetic gas theory and Kinetic gas equation,

 

KINETIC GAS THEORY


i.                   Introduction

v Matter- gaseous

v Difference between Gas and Vapour

ii.                Kinetic Molecules Theory of Gaseous

iii.              Postulate of Kinetic Gas Theory

iv.              Kinetic Gas equation

v.                 Limitation of Kinetic Theory


MATTER;

   At present on the Earth, the MATTER is classified into four types (state). They are

1.      Solid

2.     Liquid

3.     fluid 

4.    Gaseous. 

On this page, we are going to learn about the matter of  Gas, especially about the KINETIC GAS THEORY. 

  • The air around us is in the form of a gaseous state, which is the simplest state of matter.
  • Because the gaseous have no fixed shape or size,
  • And their mass and volume are not measured directly.
  • The gaseous phase of matter is generally transparent and has no definite boundaries other than those imposed by the wall of a confining vessel. Particles of a gas (atoms, molecules, or ions) are well separated, have no regular arrangement, and move freely at high speeds. Gases are compressible due to the large space in between their atoms (for molecules or ions).
  • Although the behaviour of gaseous differs depending on their composition, all gaseous exhibit strikingly similar physical behaviors.
  • The atmosphere contains a mixture of gases like nitrogen, oxygen, carbon dioxide, argon, neon, etc.

Different between Gas and Vapour:

GASEOUS

VAPOUR

Gas is a substance that is normally in a gaseous state at room temperature and 1atm pressure.

The vapour is the gaseous form of any substance that is a liquid or solid at a room temperature and 1 atm pressure.

 

 





  • To understand the molecular activity of gaseous The KINETIC THEORY OF GASEOUS plays an important role.

KINETIC MOLECULES THEORY OF GASEOUS:

  • The word "kinetic" is derived from the Greek word "kinesis", which means "MOVEMENT".
  • The kinetic gas theory explains microscopic particles (atoms and molecules) and microscopic phenomena (temperature, pressure, and volume).
  • As the kinetic theory is based upon the assumption of microscopic particles, it is sometimes referred to as a microscopical model.

The kinetic theory of gases explains how gases behave by assuming that they are made up of quickly moving atoms or molecules.

 The most basic kinetic model is based on the following assumptions.

·         The gas is made up of a large number of identical molecules moving in random directions, separated by large distances compared to their size.

·         The molecules collide completely elastically (with no energy loss) with each other and with the container walls, but otherwise do not interact.

·         Kinetic energy is transferred between molecules through heat.


POSTULATE OF KINETIC THEORY OF EQUATION:

·        Every gas consists of molecules that are microscopic particles. All the molecules of a single gas are the same and identical but differ in properties to those of other gases’ molecules.

  • ·       The size of the molecule, also known as the molecular size, is negligible as compared to the molecular distance between two molecules (which is approximately 10–9 m).
  • ·   As the molecules of gases always keep on moving (ZIG-ZAG), their molecules colloid with the walls of the containers.
  • ·     The collision between the molecules and the container walls is perfectly elastic. That is, there is no loss of kinetic energy and the velocities of molecules do not change because of collision
  • ·       As long as the molecules don’t slow down and continue to move at the same rate (constant). During the collision, there may be a redistribution of energy.
  • ·   The pressure is released due to the continuous bombardment of the molecules on the walls of the containers.
  • ·    There is no force of attraction or repulsion acting between molecules. Furthermore, gravitational force is ignored (negligible) because molecules have a tiny mass (point mass) and travel at a very high speed. They move independently of one another.
  • ·       The average kinetic energy of the gas particles is directly proportional to the absolute temperature. As a result, as the temperature rises, the average kinetic energy of the gas particles decreases. In other words, the higher the temperature, the greater the gas’s average kinetic energy.
  •    The molecules are separated by a significant amount of space. The empty spaces between the molecules are so large that the actual volume of the molecules in comparison to the total volume of the gas is negligible.
  •   Gas molecules are in constant random motion with high velocities. They move in straight lines with uniform velocities and change direction on collision with other molecules or the walls of the container.
  •    Gas molecules can move freely, independently of each other.


KINETIC GAS EQUATION:

    •  Based upon the above postulate of the kinetic Molecular theory, the KINETIC GAS EQUATION was derived. 
    •  This equation gives the relationship between temperature and average kinetic energy and is usually written in the form of
Where, 

 m -  Mass of one gas molecules
 N - Avogadro number
 u  -  velocity of gas molecules
 v  -  Volume of the gas




LIMITATIONS OF KINETIC THEORY:

    • This theory only explains ideal gases.
    •  This theory doesn’t explain real gases .   ( i.e)     H2, O2, N2  etc.
    • The natural volume of a molecule cannot be ignored.
    • These molecules attract each other.
    • In real gas molecules, the collisions are not perfectly elastic.
    • The deviation from ideal behaviour is more at low temperature and at high pressure






















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