Question

The relationship between equilibrium pressure of a gas and its amount adsorbed on the solid adsorbent at constant temperature is called (a) chemisorption (b) adsorption isobars (c) adsorption isotherms (d) none of these

Short answer

The correct answer is (c) Adsorption Isotherms.

Step-by-step solution

Understand the Terms

Adsorption refers to the process in which atoms, ions or molecules from a substance (it could be gas, liquid or dissolved solid) adhere to a surface of the adsorbent. Chemisorption is a kind of adsorption where a chemical bond is involved between the molecules and the surface. Adsorption isobars refer to the graphs between amount of gas adsorbed and pressure at constant temperature. Adsorption isotherms are curves that represent the variation of amount of gas adsorbed by the adsorbent with pressure at constant temperature.

Linking the Terms with the Question

The question is about the relationship between equilibrium pressure of a gas and its amount adsorbed on the solid adsorbent at constant temperature. This describes the scenario of an adsorption isotherm. Adsorption isotherms describe how adsorbates behave with respect to their isothermal conditions, presenting the extent of adsorption as a function of pressure at a constant temperature.

Choosing the Correct Option

Based on the understanding of terms and their link with the question, it can be concluded that the correct answer is option (c) i.e. 'Adsorption Isotherms' which best describes this relationship.

Key concepts

Adsorption

In the study of material sciences and chemistry, adsorption is a crucial process where molecules of a fluid (gas or liquid) accumulate on the surface of a solid or a liquid (adsorbent), forming a molecular or atomic film. It's essential to understand that adsorption is a surface phenomenon. The forces that drive this process could be due to Van der Waals forces (physical adsorption) or covalent bonding (chemical adsorption or chemisorption).

During adsorption, the concentration of particles increases at the adsorbent surface and establishes an equilibrium between the amount adsorbed and the remaining in the bulk phase. This equilibrium is influenced by factors such as pressure and temperature. The practical applications of adsorption are manifold, spanning from industrial gas purification to controlling humidity.

Understanding adsorption helps us to design better filtration systems, create novel materials for capturing pollutants, and even in the medical field for drug delivery systems.

Chemisorption

When we specifically look at chemisorption, we're dealing with adsorption that involves a chemical reaction between the surface and the adsorbate. This type of adsorption is particular because it results in a sturdy and often irreversible bond, similar to a chemical bond. With chemisorption, the adsorbate is held tightly to the adsorbent surface, and this can only happen at specific sites where the electronic structures of both the adsorbate and the adsorbent match favorably.

A characteristic of chemisorption is its activation energy requirement, often necessitating higher temperatures for the reaction to commence. This specificity and strength of bond are exploited in heterogeneous catalysis, where catalysts provide the necessary surface for reactants to undergo a chemical transformation.

Equilibrium Pressure

Moving on to equilibrium pressure, this term refers to the pressure at which the rate of adsorption equals the rate of desorption. It is the point where no net change occurs in the amount of substance adsorbed on the adsorbent. At this stage, a dynamic equilibrium is established in an adsorption system, and it determines the saturated surface coverage for the adsorption process.

Effect of Temperature

If the temperature of the system increases at constant equilibrium pressure, typically the amount of adsorbed substance will decrease because higher thermal energy allows the adsorbed molecules to overcome the adsorptive forces. Conversely, lowering the temperature generally allows for more adsorption to occur.

Adsorbent

Lastly, in any adsorption process, the adsorbent plays a pivotal role as the solid or liquid material that provides the surface for adsorption. An adsorbent must have a high surface area to volume ratio, which can be naturally occurring like activated carbon or synthetically made like zeolites.

Criteria for an Effective Adsorbent

An excellent adsorbent will have properties such as high porosity to provide a large surface area, suitable pore size distribution to trap the intended particles, and chemically appropriate surface properties to ensure selective and adequate attachment of the adsorbate molecules. Emerging materials like metal-organic frameworks (MOFs) are gaining attention due to their exceptional adsorptive capabilities for applications such as carbon capture and water purification.