Question

Physical adsorption is a \(\quad\) process. (a) reversible (b) irreversible (c) exothermic (d) none of these

Short answer

Physical adsorption is a reversible process, so the answer is (a) reversible.

Step-by-step solution

Understand the terms

Firstly, understand what each term means. \nReversible process refers to a process that can go back and forth between states along exactly the same path. Irreversible process is one that cannot be undone or reversed. Exothermic process is a process that releases heat into the environment. None of these would mean that none of the other options are applicable.

Understand Physical Adsorption

Physical adsorption, also called physisorption, is a process in which molecules are held on a surface due to weak van der Waals forces. This type of adsorption typically happens at low temperatures, and increases as the temperature decreases. If the temperature increases, the adsorbed molecule can gain enough energy to overcome these forces and desorb.

Find out the process type of Physical Adsorption

Based on the description in Step 2, physical adsorption is a process that can happen or be undone depending on the circumstances, particularly temperature. Therefore, it's a reversible process.

Key concepts

Reversible Process

In the world of thermodynamics, a reversible process is one where the system and its surroundings can be returned to their initial states without any net change in the overall system. This is like watching a movie in reverse where everything goes back to how it started.

For a process to be truly reversible, it must proceed infinitely slowly, allowing the system to remain in equilibrium at each step. However, in practical terms, perfect reversibility is almost impossible to achieve due to inevitable energy dissipation in the form of heat loss or friction.

Here's why reversible processes are significant:

• They allow for maximum efficiency in thermodynamic cycles. No energy is wasted.
• They are ideal models that help engineers design more efficient engines and refrigeration systems.
• Though ideal, they guide us toward creating processes that come closer to this limit.

This concept is crucial in understanding physical adsorption because it helps explain how molecules adsorb and desorb based on external conditions, like temperature changes.

Physisorption

Physisorption, also known as physical adsorption, is the process by which molecules adhere to a surface due to weak, non-specific forces known as van der Waals interactions. This contrasts with chemisorption, where the bonding is chemical and involves much stronger forces, often forming new chemical bonds.

Some key aspects of physisorption include:

• It typically occurs at relatively low temperatures, and its extent increases as temperature decreases.
• The process is usually fast and reversible, meaning that the adsorbed molecules can desorb easily without changing the chemical nature of either the adsorbate or the surface.
• The energy involved is low, which means it doesn't require much input to remove the adsorbed molecules.
• It does not involve activation energy, unlike chemisorption which requires overcoming an energy barrier.

Understanding physisorption is important because it underlines how materials can be used for gas storage, sensing, and catalysis, thanks to these weak but useful interactions.

Van der Waals Forces

Van der Waals forces are the glue that holds molecules together in physical adsorption. These forces are weak compared to chemical bonds but are crucial for numerous natural phenomena and practical applications.

Van der Waals forces can be broken down into several subtypes, including: - **Dispersion forces**, which are weak attraction forces that arise from the fluctuation of electrons around atoms. - **Dipole-dipole interactions**, occurring between polar molecules where positive and negative ends attract. - **Induced dipole forces**, when a polar molecule induces a dipole in a neighboring nonpolar molecule.
These forces allow for:

• Molecules to stack together without direct bonding.
• Reversible interactions, as seen in processes like physisorption.
• Contributing to processes such as condensation and surface tension.

Despite their weak nature, van der Waals forces play a significant role in everything from the properties of gases to the behavior of engineered materials such as carbon nanotubes and graphene.