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Question -

What is an adsorption isotherm?Describe Freundlich adsorption isotherm.



Answer -

The plot between the extent of adsorption  against the pressure of gas(P) at constant temperature (T) is called the adsorption isotherm.

Freundlich adsorptionisotherm:

Freundlich adsorption isothermgives an empirical relationship between the quantity of gas adsorbed by theunit mass of solid adsorbent and pressure at a specific temperature.

Fromthe given plot it is clear that at pressure PS, reaches the maximumvalve. Ps is called the saturation pressure. Three cases arisefrom the graph now.

Case I- At low pressure:

Theplot is straight and sloping, indicating that the pressure in directlyproportional to 
i.e.

Case II- At high pressure:

Whenpressure exceeds the saturated pressure, becomes independent of P values.

Case III- At intermediatepressure:

Atintermediate pressure,  depends on P raised to thepowers between 0 and 1. This relationship is known as the Freundlich adsorptionisotherm.
On plotting the graph between log and log P, a straight line is obtainedwith the slope
 equal to and the intercept equal to log k.

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