Which of the following is not favourable condition for physical adsorption ?

Options

A. High pressure
B. negative `DeltaH`
C. higher critical temperature of adsorbate
D. high temperature

Answer

To determine which of the following conditions is not favorable for physical adsorption, we need to analyze each option based on the characteristics of physical adsorption.

### Step-by-Step Solution:

1. **Understanding Physical Adsorption**:
- Physical adsorption is a process where gas molecules adhere to a solid surface through weak Van der Waals forces. It is generally an exothermic process, meaning it releases heat.

2. **Analyzing Conditions**:
- **High Pressure**: Increasing the pressure of a gas increases the number of gas molecules that can come into contact with the adsorbent surface. This enhances physical adsorption. Therefore, high pressure is favorable.

- **Negative Delta H**: Since physical adsorption is exothermic, it has a negative enthalpy change (ΔH < 0). This is a favorable condition for physical adsorption.

- **High Critical Temperature of Adsorbate**: A high critical temperature of the adsorbate indicates that the gas can exist in a gaseous state at higher temperatures. This condition is also favorable for physical adsorption because it allows more gas molecules to be adsorbed.

- **High Temperature**: Physical adsorption is favored at low temperatures. At high temperatures, the kinetic energy of the molecules increases, which can overcome the weak Van der Waals forces, leading to desorption. Thus, high temperature is not favorable for physical adsorption.

3. **Conclusion**:
- Among the given conditions, **high temperature** is the one that is not favorable for physical adsorption. Therefore, the correct answer is **high temperature**.

### Final Answer:
The condition that is not favorable for physical adsorption is **high temperature**.

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