Assuming multi - layer adsorption, that equation is called BET equation and this theory is called B.E.T Theory.
ASSUMPTION OF BET THEORY :-
1) The surface of adsorbed processes Uniform localised sites.
2) The adsorption at one side doesn't affect the adsorption at the neighbouring sides.
3) Adsorption is multilayer.
4) The energy of adsorption in the first layer is constant.
5) The energy of adsorption in the 2,3,4, etc layers is equal to the energy of liquification of gases.
According to BET theory,
P = 1 + ( C - 1) P
V(P⁰ − P) VmC VmC P⁰
The above equation is called BET equation (or) BET adsorption isotherm.
Here,
P = pressure of the gas
P = vapour pressure of the adsorbed liquid.
V = Total volume of gas adsorbed
Vₘ= volume of gas adsorbed at the first layer only.
C= constant.
The above equation looks like the equation of straight line. The plot of P versus P/P⁰ should give a
V(p⁰/p)
Straight line with slop C - 1
VmC
And the intercept is 1' .
VmC
The above graph is also called BET adsorption isotherm.
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Thanks for reading