The heat of adsorption of physical adsorption is nearly

Options

A. 20 - 40 kJ /mol
B. 40 - 100 kJ / mol
C. 40 - 200 kJ / mol
D. 40 - 400 kJ / mol

Answer

To solve the question regarding the heat of adsorption of physical adsorption, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Adsorption**:
- Adsorption is the process where particles (adsorbates) accumulate on the surface of a solid (adsorbent). This results in an increased concentration of the adsorbate on the surface.

**Hint**: Remember that adsorption is different from absorption; in adsorption, the particles stick to the surface rather than being absorbed into the bulk.

2. **Types of Adsorption**:
- There are two main types of adsorption: physical (physisorption) and chemical (chemisorption).
- Physical adsorption involves weak van der Waals forces, while chemical adsorption involves stronger chemical bonds.

**Hint**: Focus on the nature of the forces involved in each type of adsorption to differentiate between them.

3. **Heat of Adsorption**:
- The heat of adsorption refers to the energy released when one mole of adsorbate is adsorbed onto the adsorbent.
- In the case of physical adsorption, the forces are weak, leading to a lower amount of energy being released.

**Hint**: Recall that weaker interactions result in less energy being released compared to stronger interactions.

4. **Energy Range**:
- The heat of adsorption for physical adsorption typically falls within the range of 20 to 40 kJ per mole due to the weak van der Waals forces involved.

**Hint**: Look for the specific range given in textbooks or reliable sources to confirm the values.

5. **Specific Value**:
- In many cases, the heat of adsorption for physical adsorption is often cited as approximately 22 kJ per mole.

**Hint**: This specific value can often be found in chemistry textbooks or academic resources discussing surface chemistry.

### Final Answer:
The heat of adsorption of physical adsorption is nearly **22 kJ per mole**.