Page 2 - LN

REAL GAS:The gas which doesn’t obey all the gas laws and ideal gas equation is known as
Real gas.
 Real gases show ideal behaviour at low pressure and high temperature but at high pressure
& low temperature real gases deviate from ideal behaviour.
Compressibility factor(Z): Itis the ratio of actual molar volume of the gas to the molar
volume of the gas if it were an ideal gas.
 Value of Z for an ideal gas is zero.
Boyle temperature: The temperature at which real gases show ideal behaviour over an
appreciable change in pressure is called Boyle temperature.
Cause of deviation of real gas: The two wrong postulates of kinetic theory of gases are the
cause of deviation.
(i)The volume of each gas molecule is negligible as compared to the total volume of the gas.
(ii)There is no force of attraction between the gas molecules.
van der Waals equation of state(Real gas equation for n mole of real gas)
2
2
(p +an /V ) (V - nb) = nRT
Where a and b are van der Waals constants
 CRITICAL TEMPERATURE: The highest temperature at which a gas can be liquified is called
as critical temperature.
 CRITICAL PRESSURE: The lowest pressure at which a gas can be liquified is called critical
pressure.
 CRITICAL VOLUME: The volume occupied by one mole of a gas at its critical temperature
and critical pressure is called critical volume.
Video links :
ideal gas and real gas-https://www.youtube.com/watch?v=yZ5TudsST0w

Deviation from ideal behaviour-https://www.youtube.com/watch?v=Kp-NHNJb104

kinetic theory of gases-https://www.youtube.com/watch?v=EV6BNZ_F8zo
kinetic energy and molecular speeds-
https://www.youtube.com/watch?v=c9CRzUiDNMg

liquefaction of gases and critical phenomenon-
https://www.youtube.com/watch?v=_fvaaKOuX2s

ASSESSMENT:

1.What is the value of Z for an ideal gas?

2.At which condition real gases show ideal behaviour?

3.Write van der Waals equation of state for 1 mole of a real gas.

4.What is the relationship among most probable, average and root mean square speed.