Which of the following is less than zero during adsorption?

Options

A. `Delta G`
B. `Delta S`
C. `DeltaH`
D. `Delta H`, `Delta G` and `DeltaS`

Answer

To determine which of the following is less than zero during adsorption, we need to analyze the thermodynamic parameters involved in the process of adsorption.

### Step-by-Step Solution:

1. **Understanding Adsorption**:
- Adsorption is the process where molecules adhere to the surface of a solid or liquid. This process involves the formation of bonds between the adsorbate (the molecules being adsorbed) and the adsorbent (the surface).

**Hint**: Remember that adsorption is different from absorption; in adsorption, the molecules stick to the surface.

2. **Nature of Adsorption**:
- Adsorption is an exothermic process, which means that it releases heat. During this process, energy is released due to the formation of bonds between the adsorbate and the adsorbent.

**Hint**: Exothermic processes release energy, which can be thought of as heat being given off.

3. **Thermodynamic Parameters**:
- In thermodynamics, we often look at three key parameters:
- ΔH (enthalpy change)
- ΔS (entropy change)
- ΔG (Gibbs free energy change)

4. **Enthalpy Change (ΔH)**:
- For exothermic reactions, the enthalpy change (ΔH) is negative. This is because energy is released during the process.

**Hint**: If a process is exothermic, ΔH will be less than zero.

5. **Entropy Change (ΔS)**:
- The entropy change (ΔS) can be positive or negative depending on the system. In the case of adsorption, since the molecules are moving from a more disordered state (gas or liquid) to a more ordered state (adsorbed on a surface), ΔS is generally negative.

**Hint**: Consider how the order of molecules changes during adsorption; more order usually means less entropy.

6. **Gibbs Free Energy Change (ΔG)**:
- The Gibbs free energy change (ΔG) is given by the equation:
\[ ΔG = ΔH - TΔS \]
- For a process to be spontaneous, ΔG must be less than zero. In the case of adsorption, since ΔH is negative and ΔS is also negative, the overall sign of ΔG will depend on the temperature (T).

**Hint**: Remember that a negative ΔH and negative ΔS can lead to a negative ΔG, especially at lower temperatures.

7. **Conclusion**:
- Among the parameters ΔH, ΔS, and ΔG, the one that is always less than zero during adsorption is ΔH.

### Final Answer:
The parameter that is less than zero during adsorption is **ΔH** (enthalpy change).