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SUBJECT-CHEMISTRY

CHAPTER-STATES OF MATTER

SUB TOPIC-KINETIC THEORY OF GASES,IDEAL GAS,REAL GAS AND DEVIATION FROM IDEAL
BEHAVIOUR

KEY NOTES:
 KINETIC THEORY OF GASES:
POSTULATES:
1.Each gas consists of large number of extremely smallest particle known as gas molecules
which are identical in mass & are considered to be point masses.
2.The volume of each gas molecule is negligible as compared to the total volume of the gas.
3.Particles of a gas are always in constant & random motion in all possible direction in
straight lines.
4.During their motion, they collide with each other and also with the wall of the container.
5.Collision between the gas molecules is perfectly elastic, only redistribution of energy takes
place between the gas molecules.
6.The pressure exerted by gas molecule is due to the bombardment of the gas molecules
with the wall of the container.
7.There is no force of attraction between the gas molecules.
8.The kinetic energy of the gas molecules is a function of temperature I.e it increases with
increase in temperature.
2
KINETIC GAS EQUATION: pV =1/3mNc (where c is root mean square velocity)
DIFFERENT MOLECULAR SPEEDS
1.MOST PROBABLE SPEED: The speed possessed by maximum fraction of gas molecules at a
given temperatureis called most probable speed.
U mp = √2RT/M
2.AVERAGE SPEED – The arithmetic means of the speeds possessed by the gas molecules at
a given temperature is called average speed.
U avg = √8 /
3.ROOT MEAN SQUARE SPEED – The square root of mean of the squares of the speed
possessed by the gas molecules at a given temperature is known as root mean square
speed.

U rms = √3 /
Relationship between U mp, U avg, U rms
U mp :U avg : U rms = √2RT/M :√8 / : √3 /
= √2 :√8/ : √3 = 1 : 1.128 : 1.224
IDEAL GAS: The gas which obeys all the gas laws and ideal gas equation is known as ideal
gas