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Van der Waals forces play a crucial role in physical adsorption, acting as the weak forces of attraction between adsorbate molecules and the surface of the adsorbent. These forces are weaker compared to covalent and ionic bonds, allowing for a reversible process.
The two main components of van der Waals forces are induced dipole interactions and permanent dipole interactions.
It is these forces that facilitate the adherence of molecules onto surfaces without any significant energy changes, making physical adsorption possible.
Since the forces involved are weak, the adsorption process is generally mild and can be easily reversed just by altering conditions like temperature or pressure.

• Present in cases where no chemical bonds are formed
• Common at low temperatures where kinetic energy is minimized
• Allows for reversible adsorption

Spontaneity is a critical aspect of physical adsorption where the process occurs naturally without the need for external input. In thermodynamic terms, spontaneity is indicated when a process happens with a decrease in free energy.
For adsorption to be spontaneous, the Gibbs free energy change (\(\Delta G\)) must be negative. This implies that the overall energy landscape favors the adsorption equilibrium.
Due to the weak van der Waals interactions, physical adsorption is spontaneous even though the energy exchanged is relatively small compared to chemisorption.
This spontaneous nature ensures that as long as conditions such as temperature and pressure are suitable, the adsorption process will occur almost automatically.

Temperature has a significant effect on adsorption, especially due to the weak nature of the van der Waals forces involved.
Unlike chemical adsorption, which often strengthens with temperature, physical adsorption weakens as temperature rises. This is because increased kinetic energy from higher temperatures provides molecules with the energy needed to break free from the weak adsorptive forces.
Consequently, adsorption capacity decreases with increasing temperature, making the process less effective under warmer conditions.

• Low temperatures favor adsorption as they reduce molecular motion
• High temperatures can cause desorption of already adsorbed molecules

The thermodynamic properties of physical adsorption primarily involve changes in enthalpy (\(\Delta H\)) and entropy (\(\Delta S\)).
Both of these values are typically negative during physical adsorption.
\(\Delta H\) is negative because the process is exothermic, meaning energy is released when the adsorbate molecules adhere to the surface. This release of energy, though minor, contributes to the stabilizing factor of adsorption.
\(\Delta S\) is negative because the randomness or disorder of the system decreases.
Adsorbate molecules become more ordered as they are confined to the surface of the adsorbent, leading to a decrease in entropy. Despite the negative changes, the process remains spontaneous due to the overall decrease in Gibbs free energy, affirming the natural tendency for adsorption to occur.