Adsorption is accompanied by

Options

A. decrease in entropy of the system
B. decrease in enthalpy of the system
C. TDS for the process is negative
D. All of these

Answer

**Step-by-Step Solution:**

1. **Definition of Adsorption:**
- Adsorption is the process where molecules (adsorbate) accumulate on the surface of a solid or liquid (adsorbent) rather than being distributed throughout the bulk.

2. **Nature of the Process:**
- Adsorption is an exothermic process. This means that during adsorption, energy is released, resulting in a negative change in enthalpy (ΔH < 0).

3. **Entropy Change:**
- As molecules are adsorbed onto the surface, the randomness or disorder of the system decreases. This leads to a negative change in entropy (ΔS < 0).

4. **Gibbs Free Energy:**
- For a process to be spontaneous, the change in Gibbs free energy (ΔG) must be negative. The relationship is given by the equation:
\[ \Delta G = \Delta H - T \Delta S \]
- Since ΔH is negative and ΔS is also negative, the term \(T \Delta S\) will also be negative (as T is always positive).

5. **Condition for Spontaneity:**
- For the process to be spontaneous, the magnitude of ΔH must be greater than the magnitude of \(T \Delta S\) to ensure that ΔG remains negative. Thus, we can conclude that:
\[ \Delta G < 0 \quad \text{(spontaneous process)} \]

6. **Conclusion:**
- Therefore, adsorption is accompanied by a release of energy (exothermic), a decrease in entropy, and results in a negative Gibbs free energy change, confirming that it is a spontaneous process.

**Final Answer:**
Adsorption is accompanied by a decrease in enthalpy (exothermic process) and a decrease in entropy.

---