Which of the following is true in respect of adsorption

Options

A. `DeltaGlt0,DeltaSgt0,DeltaHlt0`
B. `DeltaGlt0,DeltaSlt0,DeltaHlt0`
C. `DeltaGgt0,DeltaSgt0,DeltaHlt0`
D. `DeltaGlt0,DeltaSlt0,DeltaHgt0`

Answer

To determine which statement is true regarding adsorption, we can analyze the concept step by step.

### Step-by-Step Solution:

1. **Definition of Adsorption**:
- Adsorption is the process where molecules of a substance (adsorbate) accumulate on the surface of another substance (adsorbent), forming a film or coating.

2. **Types of Adsorption**:
- There are two main types of adsorption:
- **Physisorption**: This involves weak Van der Waals forces. It is a physical process where gas molecules adhere to the surface of a solid.
- **Chemisorption**: This involves the formation of chemical bonds. It is a stronger process compared to physisorption.

3. **Entropy Change in Adsorption**:
- During adsorption, the molecules of the adsorbate are held on the surface of the adsorbent, leading to a decrease in entropy (ΔS < 0). This is because the freedom of movement of the adsorbate molecules is restricted when they adhere to the surface.

4. **Gibbs Free Energy**:
- The Gibbs free energy change (ΔG) is related to enthalpy (ΔH) and entropy (ΔS) by the equation:
\[ \Delta G = \Delta H - T \Delta S \]
- For the adsorption process to be spontaneous, ΔG must be negative. Given that ΔS is negative, for ΔG to remain negative, ΔH must also be sufficiently negative (exothermic process).

5. **Exothermic Nature of Adsorption**:
- Generally, adsorption is an exothermic process, meaning it releases heat. However, in some cases, chemisorption can be endothermic, but typically, it is considered exothermic.

6. **Conclusion**:
- The correct statement regarding adsorption is that it is a process where the adsorbate accumulates on the adsorbent surface, leading to a decrease in entropy and is generally exothermic.

### Final Answer:
The true statement regarding adsorption is that it involves the accumulation of molecules on the surface of another substance, leading to a decrease in entropy and is generally an exothermic process.