Question
What are the main differences between physical adsorption and chemical adsorption ?
| Physical Adsorption | Chemical Adsorption | |
| 1. | It involves weak physical forces of attraction between adsorbate and adsorbent, i.e., van der Waals forces. It is an exothermic process. | It involves transfer of electrons between adsorbate and adsorbent, i.e., the forces operating are similar to those of a chemical bond. It is also exothermic. |
| 2. | Physisorption forms multi-molecular layers. | Chemisorption forms unimolecular layer. |
| 3. | More easily liquifiable gases are adsorbed readily | The gases which form compounds with the adsorbent are only chemisorbed. |
| 4. | Heat of adsorption is low (about 20-40 kJ mol¹). | Heat of adsorption is high (about 40-400 kJ mol¹). |
| 5. | It is not specific in nature as all types of gas are adsorbed on all solids by weak van der waals forces. It depends on polar nature of adsorbates roughness of surface of adsorbent. | It is highly specific in nature and occurs only when there is some possibility of compound formation between the adsorbate and adsorbent. |
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3d34s2, 3d54s2 and 3d6 4s3. Indicate relative stability of oxidation states in each case.
| Column I | Column II | ||
| i. | Raoult’s law | a. | $\Delta\text{T}_\text{f}=\text{K}_\text{f}\text{m}$ |
| ii. | Henry’s law | b. | $\pi=\text{CRT}$ |
| iii. | Elevation of boiling point | c. | $\text{p}=\text{x}_1\text{p}^0_1+\text{x}_2\text{p}^0_2$ |
| iv. | Depression in freezing point | d. | $\Delta\text{T}_\text{b}=\text{K}_\text{b}\text{m}$ |
| v. | Osmotic pressure | e. | $\text{p}=\text{K}_\text{H}\cdot\text{x}$ |
| | Column I |
| Column II |
| i. | $\text{K}$ | a. | $\text{I}\times\text{t}$ |
| ii. | $\wedge_{\text{m}}$ | b. | $\frac{\wedge_{\text{m}}}{\wedge^\circ_\text{m}}$ |
| iii. | $\alpha$ | c. | $\frac{\text{k}}{\text{c}}$ |
| iv. | $\text{Q}$ | d. | $\frac{\text{G}^*}{\text{R}}$ |