What are the factors affecting adsorption of gases on solids?

What are the factors affecting adsorption of gases on solids?


2 Answers

askIITIians Expert
21 Points
15 years ago

Factors affecting adsorption of gases on solids

(1)    Nature of adsorbate: Physical adsorption is non – specific in nature and therefore every gas gets adsorbed on the surface of any solid to a lesser or greater exetent. However, easily liquefiable gases like NH3, HCL, Co2 etc are adsorbed to greater extent whereas H2, O2, N2 etc are adsorbed to lesser extent.


(2)    Nature of Adsorbent: Activated carbon, metal oxides like aluminum oxide, silica gel and clay are commonly used adsorbents. They have their specific adsorption properties depending upon pores.


(3)    Specific area of the adsorbent: The greater the specific area, more will be the extent of adsorption. That is why porous or finely divided forms of adsorbents adsorb larger quantities of adsorbate.


(4)    Pressure of the gas: Physical adsorption increases with increase in pressure. The extent of adsorption is expressed as x/m where ‘x’ is amount of adsorbate. ‘m’ is mass of adsorbent when the dynamic equilibrium is established between free gas and the adsorbed gas.

Akshay Malhotra
19 Points
8 years ago
Factors affecting adsorption of gas on solids
We know that adsorption is an exothermic reaction. So, when temperature is increased then the equilbrium shifts in backward direction and in this way rate of adsorption decreases with increase in temperature.
Now to be more specific, in physical adsorption the rate of adsorption decreases continously. In case of chemical adsorption firstly the rate of adsorption increases (the reason behind this is that increase in temperature leads to giving in activation energy of reaction) but after a certain temperature the rate of adsorption decreases (the reason is that when the reaction gets required activation energy and the bonds are formed then if more temperature is risen then the bonds will start breaking leading to the decrease in rate of adsorption).
When pressure is increased then the rate of adsorption increases. The reason behind this is given as follows.
When presssure is increased then according to Le Chatlier's principle, the equilbrium shifts in the direction to reduce pressure that is in that direction where the number of moles is less that is the equilbrium will shift in the forward direction.
Activation of adsorbent
It basically means to increase the capacity of adsorption.
It can be done in 3 given ways – 
  1. By making the surface of adsorbent rough.
  2. By heating the adsorbent in vacuum so that the water vapour present in pores leave those pores.
  3. By increasing the surface area of adsorbent.
Nature of adsorbate
Polar molecules have high value of [a] factor (this factor iss present in van der waals equation). When the value of [a] is high then the force of attraction among the molecules of the polar molecules increases which leads to the high critical temperature of the gases(critical temperature is that temperature above which a gas cannot be liquified even how many atmospheres of pressure is applied). Now, higher the critical temperature of the liquids the higher will be the rate of adsorption of the gas.
Now the explanation reverse of it we can say that non polar molecules do not have high rate of adsorption.
Surface area of adsorbate
The larger the surface area of adsrbent more is the adsorption.

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