Which of the following statement is not correct?

Options

A. Physical adsorption is due to van der Waal’s force
B. Chemical adsorption decreases at high temperature and low pressure
C. Physical adsorption is reversible
D. Heat of adsorption for chemical adsorption is generally greater than that of physical adsorption.

Answer

To determine which statement is not correct regarding physical and chemical adsorption, we need to analyze each statement based on the principles of surface chemistry.

### Step-by-Step Solution:

1. **Understanding Adsorption**:
- Adsorption is the process where particles accumulate on the surface of a solid. It can occur with gases, liquids, or solids.

2. **Types of Adsorption**:
- **Physical Adsorption**: Involves weak van der Waals forces. It is generally reversible and can be easily broken by increasing temperature or reducing pressure.
- **Chemical Adsorption**: Involves the formation of strong chemical bonds. This process is usually irreversible and requires a significant amount of energy to break the bonds.

3. **Analyzing the Statements**:
- **Statement 1**: "Chemical adsorption is due to van der Waals forces."
- This statement is incorrect because chemical adsorption is due to the formation of strong chemical bonds, not van der Waals forces.

- **Statement 2**: "Chemical adsorption decreases at high temperature and low pressure."
- This statement is correct. Increasing temperature generally provides more energy to molecules, which can enhance chemical reactions and adsorption initially, but at very high temperatures, it can lead to desorption.

- **Statement 3**: "Physical adsorption is reversible."
- This statement is correct. Physical adsorption can be reversed easily by changing temperature or pressure.

- **Statement 4**: "Heat of adsorption for chemical adsorption is generally greater than that of physical adsorption."
- This statement is correct. The energy released during chemical adsorption is higher due to the formation of strong bonds compared to the weak interactions in physical adsorption.

4. **Conclusion**:
- The statement that is not correct is **Statement 1**: "Chemical adsorption is due to van der Waals forces."

### Final Answer:
The incorrect statement is: **"Chemical adsorption is due to van der Waals forces."**