Which of the following is true is respect of chemical adsorption (chemisorption)?

Options

A. `∆Hlt0, ∆Sgt0, ∆Ggt0`
B. `∆Hlt0, ∆Slt0, ∆Glt0`
C. `∆Hgt0, ∆Sgt0, ∆Glt0`
D. `∆Hgt0, ∆Slt0, ∆Ggt0`

Answer

To determine which statement is true regarding chemical adsorption (chemisorption), we can analyze the characteristics and thermodynamic principles associated with this process. Here’s a step-by-step solution:

### Step 1: Understand the Definition of Chemisorption
Chemisorption refers to the process where a gas or liquid molecule forms a strong chemical bond with a solid surface. This process is typically characterized by the formation of covalent or ionic bonds.

**Hint:** Remember that chemisorption involves strong interactions, unlike physisorption, which involves weaker van der Waals forces.

### Step 2: Analyze Energy Changes
During chemisorption, energy is released as bonds are formed between the adsorbate and the surface. This release of energy indicates that the process is exothermic.

**Hint:** Exothermic reactions release energy, leading to a negative change in enthalpy (ΔH < 0).

### Step 3: Consider Entropy Changes
When gas molecules adhere to a solid surface, their freedom of movement is restricted. This results in a decrease in randomness or disorder of the system, which means that the entropy (S) of the system decreases.

**Hint:** A decrease in randomness implies a decrease in entropy (ΔS < 0).

### Step 4: Apply Gibbs Free Energy Concept
The Gibbs free energy change (ΔG) for a process is given by the equation:
\[ \Delta G = \Delta H - T\Delta S \]
For a spontaneous process, ΔG must be negative. Since ΔH is negative (exothermic) and ΔS is negative (decreased randomness), the overall sign of ΔG depends on the temperature and the magnitudes of ΔH and ΔS.

**Hint:** A negative ΔH and a negative ΔS can still lead to a negative ΔG under certain conditions, particularly at low temperatures.

### Step 5: Conclusion
Based on the analysis:
- The enthalpy change (ΔH) is negative because energy is released.
- The entropy change (ΔS) is negative because the randomness decreases.
- Therefore, the statement that is true regarding chemisorption is that it involves a negative enthalpy change and a negative entropy change.

**Final Answer:** The correct statement regarding chemical adsorption (chemisorption) is that the enthalpy change is negative, indicating that energy is released during the process.