Which adsorption takes place at low temperature?

Answer

To determine which type of adsorption occurs at low temperatures, we will analyze the characteristics of both physisorption and chemisorption.

### Step-by-Step Solution:

1. **Understanding Adsorption**:
- Adsorption is the process where molecules accumulate on the surface of a solid or liquid, rather than in the bulk.
- There are two main types of adsorption: physisorption and chemisorption.

**Hint**: Remember that adsorption involves surface interactions, not bulk interactions.

2. **Physisorption**:
- Physisorption occurs due to weak van der Waals forces of attraction.
- It is generally a reversible process and is not specific to the type of gas or solid involved.
- The process is exothermic, meaning that heat is released when a gas is adsorbed onto a solid.

**Hint**: Think of physisorption as a weak, temporary bond that can easily be broken.

3. **Chemisorption**:
- Chemisorption involves the formation of strong chemical bonds between the adsorbate and the surface.
- This process is specific to the type of molecules involved and is generally irreversible.
- While chemisorption is also exothermic, it requires higher activation energy, making it a slower process at lower temperatures.

**Hint**: Chemisorption is like a strong, permanent bond that requires more energy to form.

4. **Temperature Effects**:
- According to Le Chatelier's principle, if a reaction is exothermic and the temperature is increased, the equilibrium will shift to favor the reactants (backward direction).
- Conversely, at lower temperatures, the equilibrium shifts to favor the products (forward direction), enhancing the adsorption process.

**Hint**: Consider how temperature affects the energy and speed of molecular interactions.

5. **Conclusion**:
- Since physisorption is favored at low temperatures due to its exothermic nature and reversible process, it is the type of adsorption that occurs at low temperatures.
- Chemisorption, on the other hand, requires higher temperatures to overcome the activation energy barrier.

**Final Answer**: Physisorption takes place at low temperature.