What is the effect on entropy change `(triangle S)` in adsorption?

Answer

### Step-by-Step Text Solution:

1. **Understanding Entropy**:
- Entropy (ΔS) is a measure of the randomness or disorder of a system. Higher entropy indicates greater disorder, while lower entropy indicates more order.

2. **Before Adsorption**:
- Consider a scenario where gas molecules are present in a system without any adsorption occurring. In this state, the gas molecules can move freely and randomly in the space available to them.
- This free movement results in a high degree of randomness, meaning that the entropy of the system is at its maximum.

3. **During Adsorption**:
- When adsorption occurs, gas molecules (adsorbate) adhere to the surface of a solid (adsorbent). This process involves the gas molecules interacting with the solid surface.
- As the gas molecules become adsorbed, their movement is restricted because they are now bound to the surface of the solid. This leads to a decrease in the randomness of the gas molecules.

4. **Effect on Entropy Change**:
- Due to the restricted movement and the formation of ordered structures between the adsorbate and adsorbent, the overall disorder of the system decreases.
- Therefore, the change in entropy (ΔS) during adsorption is negative (ΔS < 0). This indicates a decrease in randomness and an increase in order.

5. **Conclusion**:
- In summary, the effect on entropy change during adsorption is a decrease in entropy, resulting in a negative change in entropy (ΔS < 0) due to the association between adsorbate and adsorbent.