Difference between physical adsorption and chemisorption are as following:
|
PHYSICAL ADSORPTION |
CHEMISORPTIONS |
| The forces operating in these are weak vander Waal’s forces. | The forces operating in these cases are similar to those of a chemical bond. |
| The heat of adsorption are low i.e. about 20 – 40 kJ mol-1 | The heat of adsorption are high i.e. about 40 – 400 kJ mol-1 |
| No compound formation takes place in these cases. | Surface compounds are formed. |
| The process is reversible i.e. desorption of the gas occurs by increasing the temperature or decreasing the pressure. | The process is irreversible. Efforts to free the adsorbed gas give some definite compound. |
| It does not require any activation energy. | It requires any activation energy. |
| This type of adsorption decreases with increase of temperature. | This type of adsorption first increases with increase of temperature. The effect is called activated adsorption. |
| It is not specific in nature i.e. all gases are adsorbed on all solids to some extent. | It is specific in nature and occurs only when there is some possibility of compound formation between the gas being adsorbed and the solid adsorbent. |
| The amount of the gas adsorbed is related to the ease of liquefaction of the gas. | There is no such correlation exists. |
| It forms multimolecular layer. | It forms unimolecular layer. |
