Physical adsorption of a gaseous species may change to chemical adsorption with

Options

A. decrease in temperature
B. increase in temperature
C. increase in surface area of adsorbent
D. decrease in surface area of adsorbent

Answer

To solve the question regarding the transition of physical adsorption to chemical adsorption, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Physical and Chemical Adsorption**:
- Physical adsorption (physisorption) is a weak interaction between the adsorbate and the adsorbent, primarily due to van der Waals forces.
- Chemical adsorption (chemisorption) involves the formation of stronger chemical bonds between the adsorbate and the adsorbent.

2. **Role of Temperature**:
- The question asks how physical adsorption can change to chemical adsorption. One of the key factors that can influence this transition is temperature.
- Typically, increasing the temperature can provide enough energy to overcome the weak forces of physical adsorption.

3. **Enthalpy Changes**:
- The enthalpy change (ΔH) for physical adsorption is generally in the range of -20 to -80 kJ/mol.
- For chemical adsorption, the enthalpy change is much higher, ranging from -80 to -400 kJ/mol.
- To transition from physical to chemical adsorption, the energy must be sufficient to reach the higher enthalpy state associated with chemical adsorption.

4. **Activation Energy**:
- As temperature increases, the kinetic energy of the adsorbate molecules increases, which can lead to an increase in the activation energy.
- This increase in energy can facilitate the formation of stronger chemical bonds between the adsorbate and the adsorbent.

5. **Conclusion**:
- Therefore, the correct answer to the question is that physical adsorption may change to chemical adsorption with an **increase in temperature**.

### Final Answer:
The physical adsorption of a gaseous species may change to chemical adsorption with an **increase in temperature**.

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