Adsorption is accompanied by

Options

A. Langmuir adsorption is highly specific
B. Vander waal's adsorption is reversible
C. Both 1 and 2 are exothermic
D. All are correct

Answer

**Step-by-Step Solution:**

1. **Understanding Adsorption**: Adsorption is the process where atoms, ions, or molecules from a gas, liquid, or dissolved solid adhere to a surface. This process can be classified into two main types: physical adsorption (physisorption) and chemical adsorption (chemisorption).

2. **Types of Adsorption**:
- **Physical Adsorption (Physisorption)**: This type of adsorption occurs due to weak Van der Waals forces. It is generally reversible and does not involve a significant change in the electronic structure of the adsorbate.
- **Chemical Adsorption (Chemisorption)**: This involves the formation of strong chemical bonds between the adsorbate and the adsorbent. It is usually irreversible and involves a significant energy change.

3. **Characteristics of Adsorption**:
- **Exothermic Process**: Both types of adsorption release energy in the form of heat, making them exothermic processes. This means that as the adsorbate adheres to the surface of the adsorbent, heat is released.
- **Equilibrium**: In the case of Langmuir adsorption, there is a specific equilibrium established between the adsorbate and the adsorbent. The adsorption is limited to a single molecular layer, and the relative pressure should not exceed unity (1).

4. **Reversibility**:
- Physical adsorption is reversible, which means that the adsorbate can be removed from the adsorbent by applying heat or reducing the pressure.
- Chemical adsorption is typically not reversible under normal conditions.

5. **Conclusion**: Based on the characteristics of adsorption discussed, we can conclude that:
- Both physical and chemical adsorption are exothermic processes.
- Physical adsorption is reversible, while chemical adsorption is not.
- The Langmuir adsorption model describes a specific type of adsorption that is highly specific and limited to one molecular layer.

6. **Final Answer**: Since all statements regarding adsorption (1st, 2nd, and 3rd) are correct, the answer to the question "Adsorption is accompanied by" is that it is accompanied by exothermic processes and can be reversible in the case of physical adsorption.

---