The rate of chemisorption (a) decreases with increase of pressure (b) is independent of pressure (c) is maximum at one atmospheric pressure (d) increases with increase of pressure

Short Answer

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The rate of chemisorption increases with the increase of pressure due to more adsorbate molecules being available near the surface until the surface becomes saturated.

Step by step solution

01

Understanding Chemisorption

Chemisorption is a type of adsorption that involves a chemical reaction between the surface and the adsorbate. In chemisorption, adsorbate molecules form strong chemical bonds with the surface atoms. This process is highly specific and usually takes place at specific sites on the surface.
02

Assessing the Effects of Pressure on Adsorption

According to Le Chatelier's principle, for any system in dynamic equilibrium, if a change (such as pressure, temperature, or concentration) is applied to the system, the system adjusts itself to partially counteract the applied change and restore equilibrium. In chemisorption, when pressure increases, the concentration of adsorbate molecules near the surface increases, leading to more molecules being chemisorbed up to a certain limit.
03

Interpreting the Effect of Pressure on Chemisorption Rate

Chemisorption initially increases with an increase in pressure because more adsorbate molecules are in proximity to the adsorption sites, increasing the probability of adsorption. However, after a certain point, the surface becomes saturated, and the rate of chemisorption does not increase significantly with pressure. Therefore, option (d) 'increases with increase of pressure' is the most appropriate choice before reaching saturation.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Le Chatelier's Principle
Le Chatelier's principle is a fundamental concept in chemistry that explains how dynamic systems respond to external changes to maintain equilibrium. When any system at equilibrium experiences a change in concentration, temperature, or pressure, the system adjusts in a way to counteract that change.

Take the scenario of a reversible chemical reaction in equilibrium. If you increase the pressure, the reaction will shift to the side with fewer gas molecules, minimizing the change. This principle directly relates to chemisorption, where the adsorption rate changes as a result of pressure variations. Increasing the pressure pushes the system to adsorb more gas molecules, thus favoring the adsorption process, up to a point where the surface is saturated.
Adsorption
Adsorption is a process where molecules from a gas or liquid phase adhere to a solid surface. This phenomenon occurs due to the surface energy that creates a potential for molecules to stick to the surface.

There are two types of adsorption, physisorption and chemisorption. Physisorption involves weak van der Waals forces, whereas chemisorption involves the formation of strong chemical bonds. Understanding adsorption is vital in many industrial processes, such as catalysis, where the rate of a chemical reaction is increased by the presence of a solid surface that adsorbs reactants.
Dynamic Equilibrium
Dynamic equilibrium occurs in a closed system when the rate of the forward reaction equals the rate of the reverse reaction. This results in no net change in the concentration of reactants and products over time, even though individual molecules continue to react.

A system at dynamic equilibrium is sensitive to external changes. According to Le Chatelier's principle, increasing pressure on a system at equilibrium will shift the reaction to accommodate this change, affecting both chemisorption rates and other equilibrium processes.
Surface Saturation
Surface saturation refers to the state of a solid surface when it has adsorbed the maximum number of adsorbate molecules and can no longer adsorb additional molecules. At this point, the adsorbate forms a complete layer on the adsorbent surface, and the surface's active sites are fully occupied.

Increasing pressure doesn't affect the chemisorption rate after the surface saturation point because there are no free sites left for additional molecules to adhere to. This concept is crucial to understanding the limitations of adsorption-based processes, including catalysis and filtration.

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