The document discusses adsorption, which is the accumulation of molecules on the surface of solids or liquids. It defines key terms like adsorbate, adsorbent, desorption, and occlusion. The document also distinguishes between physisorption and chemisorption, and notes factors that influence adsorption like surface area, temperature, and pressure. Some applications of adsorption are mentioned as well, such as in gas masks, vacuum production, water softening, catalysis, petroleum refining, and chromatography.

2. Dr. SURENDRAN PARAMBADATH
(M.Sc, M.Phil, M.Tech)
Formerly: Post Doctoral Research Associate,
Nano-Information Materials Research Laboratory,
Pusan National University, Busan-South Korea
Currently: Assistant Professor
Govt. Polytechnic College, Perinthalmanna

3. Bulk Surface

4. Surface of solids and liquids
has the tendency to attract
and retain other molecules
with which it is brought in to
contact.

6. This is due to unbalanced
residual inward forces of
attraction or free valencies
at the surface of solids and
liquids.

7. Due to these residual forces,
surface of solid or liquid has
a higher concentration of
other molecular species than
the bulk.

9. Adsorbed material
Free materials

11. Adsorption: The accumulation
of molecular species at the
surface of a solid or liquid
rather than in the bulk is called
adsorption.

13. Adsorbate: The molecular
species that accumulate at the
surface is termed adsorbate.
Adsorbate

14. Adsorbent: The material on the
surface of which adsorption
takes place is called
adsorbent.
Adsorben
t

15. Desorption: The removal of
adsorbate from the surface is
called desorption.

16. Occlusion: The adsorption of
gases on the surface of metals
is called occlusion.

17. Examples for adsorption…………
1. If a gas like H2, O2, Cl2 etc is taken in a vessel
containing powdered charcoal, pressure of the gas
slowly decreases as the gas is adsorbed on the surface
of charcoal.
2. Air becomes dry in presence of silica gel because
adsorption of water takes place on the surface of the
gel.
3. Aqueous solution of raw sugar becomes colourless
when passed over a bed of animal charcoal. The
coloring matter is adsorbed by the charcoal.
4. Litmus solution or a solution of a dye like methylene
blue when shaken with animal charcoal turns
colourless due to adsorption of coloring material.

19. Absorption:

20. Sorption:

21. Distinction between adsorption & Absorption
Adsorption Absorption
It is a surface It is a bulk phenomenon
phenomenon
Adsorbed species is It is uniformly distributed
accumulated in the throughout the bulk
surface
It is a fast process It is a slow processes
Rate of adsorption Absorption takes place at
decreases gradually steady rate

23. Physisorption Chemisorption

25. If accumulation of gas molecules on
the surface of solids occurs due to
weak van der Waals’ forces of
attraction, the adsorption is called
physisorption.

27. When atoms or molecules of gases
are held by solids on its surface by
chemical bonds, the adsorption is
called chemisorption.

28. Characteristics of Physisorption
1. Non-specific nature: An adsorbent does not show any preference
for a gas as the van der Waals’ forces are universal.
2. Easily liquefiable gases like CO2, SO2, NH3 etc, are readily
adsorbed.
3. Reversible nature: Physisortion of a gas by a solid is reversible.
4. Increases by increase of pressure.
5. Surface area of adsorbant: When the surface area of the adsorbent
increases, more gas is adsorbed, ie extent of adsorption increases.
6. Enthalpy of adsorption: Enthalpy of adsorption of physisorption
is very low (20-40 KJ mol-1)
Since adsorption is exothermic, physisorption takes place
readily at low temperature and desorption takes place at higher
temperature.

29. Characteristics of Chemisorption
1. High specificity: It is highly specific and will occur only
if chemical bond formation takes between adsorbate and
adsorbent.
2. Irreversibility: Chemisorption is irreversible because the
chemical bond formed is difficult to break.
3. Chemisorption increases with temperature.
4. Increases by increase of pressure.
5. Surface area of adsorbent: When the surface area of the
adsorbent increases, more gas is adsorbed, ie extent of
adsorption increases.
6. Enthalpy of adsorption: Enthalpy of adsorption of
chemisorption is high (80-240 KJ mol-1)

30. Physisorption Chemisorption
1 Occurs due to van der Waals’ force Chemical Bond
2 Reversible Irreversible
3 Not specific Specific
4 Enthalpy of adsorption is low Enthalpy of adsorption is high
5 More liquefiable gases are adsorbed Gases which form compounds with
readily adsorbent alone undergo chemisorption
6 Decreases with increase of temperature Increases with increase of temperature
7 Low temperature is favorable. High temperature is favorable
8 High pressure favors physisorption and High pressure is favorable but decreases of
decrease of pressure causes desorption pressure does not cause desorption
9 Results in multimolecular layers Only unimolecular layer are formed
10 No activation energy is needed High activation energy is needed
11 It is instantaneous It is a slow process

31. Factors Influencing
Adsorption

32. 2. Surface Area of the Adsorbent
Same gas is adsorbed to different extent by
different solids at identical conditions. Greater
the surface area of the adsorbent greater the
volume of gas adsorbed.

33. 3. Temperature
Adsorption of a gas generally decreases with
rise in temperature. This is because adsorption
is exothermic and increases of temperature
favors the backward process which is
desorption.
Heat

34. 4. Pressure
Adsorption of a gas by an adsorbent at constant
temperature increases with increase of
pressure.

35. Applications
Adsorption

36. 1. In Gas Masks

38. 2. Production of High
Vacuum

39. 3. Softening of Hard
water
Ca2+ Ca2+ Ca2+ Ca2+
Exchange
resin

40. 4. Heterogeneous
Catalysis

41. 5. Refining of Petroleum

43. 6. Chromatographic Seperation