Which of the following is not a characteristic of chemisorption ?

Options

A. lrreversible nautre
B. `Delta ` H is the order of 500 J
C. Specific in nature
D. Increases with increase of surface area

Answer

To determine which of the following is not a characteristic of chemisorption, we need to understand the key features of chemisorption. Here’s a step-by-step breakdown of the characteristics of chemisorption:

### Step 1: Definition of Chemisorption
Chemisorption, or chemical adsorption, involves the formation of strong chemical bonds between the adsorbate (the substance being adsorbed) and the surface of the adsorbent (the material on which adsorption occurs). This process is different from physisorption, which involves weak van der Waals forces.

**Hint:** Remember that chemisorption involves strong chemical bonds, while physisorption involves weak forces.

### Step 2: Characteristics of Chemisorption
1. **Strong Bond Formation:** Chemisorption involves the formation of strong bonds (covalent or ionic) between the adsorbate and the adsorbent.

**Hint:** Think about the strength of the bonds formed during chemisorption compared to physical adsorption.

2. **Irreversibility:** Chemisorption is generally irreversible because the strong bonds formed are difficult to break. Once the adsorbate is attached, it does not easily detach from the surface.

**Hint:** Consider what happens to the bonds formed during chemisorption—are they easy to break?

3. **Activation Energy Requirement:** For chemisorption to occur, a certain amount of activation energy is required. This energy is necessary to overcome the energy barrier for bond formation.

**Hint:** Recall that chemical reactions often require energy to initiate bond formation.

4. **Specificity:** Chemisorption is specific to particular adsorbates and adsorbents due to the nature of the chemical bonds formed.

**Hint:** Think about how not all substances will chemisorb to every surface—there's a selectivity involved.

5. **Heat of Adsorption:** The heat of adsorption for chemisorption is typically higher than that for physisorption, often in the range of 80-240 kJ/mol.

**Hint:** Remember that the energy released during chemisorption is significant compared to physical adsorption.

### Step 3: Identify the Incorrect Characteristic
Now, we need to identify which characteristic does not belong to chemisorption. The question suggests that one of the options does not fit the characteristics discussed.

- If one of the options states that the heat of adsorption is around 500 kJ/mol, this would be incorrect because typical values range from 80-240 kJ/mol.

### Conclusion
Thus, the characteristic that is not true for chemisorption is that the heat of adsorption is around 500 kJ/mol.

**Final Answer:** The characteristic that is not true for chemisorption is that the heat of adsorption is 500 kJ/mol.