Adsorption
Chapter Name : Surface Chemistry |
Sub Topic Code : 102_12_05_02_04 |
Topic Name : Adsorption |
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Sub Topic Name : Types Of Adsorption |
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Introduction
• When the force of attraction existing between adsorbate and adsorbent are weak Vander Waal forces of attraction, the process is called Physical Adsorption or Physisorption. It has low enthalpy of adsorption i.e. ?H = 20-40KJ/mol. Also it takes place at low temperature. As the temperature increases, process of physisorption decreases. • When the force of attraction existing between adsorbate and adsorbent are chemical forces of attraction or chemical bond, the process is called Chemical Adsorption or Chemisorption. It has high enthalpy of adsorption i.e. ?H = 80-240 KJ/mol. Also it takes place at high temperature. With the increase in temperature, chemisorption increases.
Pre-Requisites:
• Introduction of adsorption • Adsorption mechanism
Activity:
If a sachet of silica gel is kept near a pot of boiling water, all the water vapor generated due to boiling gets adsorbed by the silica gel. This is an example of physical adsorption. On the other hand, rusting of iron when exposed to water vapour is an example of chemical adsorption.
Real Life Question:
How do the adsorbate particles attach themselves to the adsorbents?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Adsorption | It is the phenomenon of accumulation of molecules of a liquid/gas on the surface of a solid. |
| Adsorbate | It is the substance which concentrates or accumulates at the surface of another substance. |
| Adsorbent | It is the substance on which adsorption occurs i.e. on which another substance gets accumulated. |
| Physisorption | When the forces of attraction existing between the adsorbate and the adsorbent are Vander Waal’s forces, the adsorption is called physical adsorption. |
| Chemisorption | When the forces of attraction existing between the adsorbate particles and the adsorbent are almost of the same strength as chemical bonds, the adsorption is called chemical adsorption. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Silica gel | Keep a sachet of silica gel near a pot of boiling water. |
| A pot of boiling water | For generation of water vapour. |
| Rusted iron bar | Observe it. |
Real life uses :
Treatment of waste water, controlling humidity.
Places to visit :
Water treatment plant.
Practical examples around us
| Examples | Explainations |
|---|---|
| Water treatment plant | Cleaning of wastewater is done using activated carbon (char-like material). Pollutants in the water get physically adsorbed on the surface of carbon leading to cleansing of water. |
What you learn in Theory:
The various ways in which a gas can get adsorbed to a solid.