Laws Of Kinetic Theory Of Gases

Card # 41‐Laws of Kinetic Theory of Gases The state of a gas can be represented by three quantities pressure, volume and temperature. The relationships between three quantities resulted in three laws - Keeping pressure constant, changes in volume with temperature (Charles’s law) - Keeping temperature constant, changes in volume with pressure (Boyle’s law) - Keeping volume constant, change in pressure with temperature (Law of pressure) Boyle’s Law According to this law at constant temperature for a fixed mass of a gas, the volume of a gas is inversely proportional to the pressure

V

1 p

α

or V

=

k p

PV = k Boyle’s law is perfectly obeyed at high temperature and low pressure but at high pressure and low temperature. Boyle’s law does not hold well, there is deviation in experimental and theoretical graphs. Charles’s law If pressure is kept constant, the volume of given mass of a gas increases with temperature at a nearly constant rate

V

α

T

,

V T

 

= c o n s ta n t

Law of Pressure Volume remaining constant, the pressure of a given mass of a gas is directly proportional to its absolute temperature i.e. P α T , P/T = constant Ideal gas equation The gas which obeys Boyle’s and Charles’s law is called ideal gas. Both laws can be combined to obtain the general relationship between P, V and T for a given mass. This relation is called perfect gas equation

1 T

From Boyle’s law V

α

α Charles’s law V V = constant T/P PV = Constant T

T

P

V

=

n R

T

Here n = m/M = mass of the gas = Number of moles Atomic or molecular mass of gas R = Universal gas constant = 8.31 Jmol −1k −1