Surface phenomena: Chemisorption (chemical adsorption) is best described by which characteristic?

Introduction:
Adsorption involves accumulation of molecules at surfaces and is broadly categorized into physisorption (Van der Waals) and chemisorption (chemical bonding). Distinguishing their key traits guides catalyst selection, surface treatment, and sensor design.

Given Data / Assumptions:

• Chemisorption forms chemical bonds between adsorbate and surface sites.
• Physisorption arises from weak Van der Waals forces.
• Temperature effects and reversibility differ markedly between the two.

Concept / Approach:
Chemisorption typically involves higher heats of adsorption, site specificity, possible activation energy, and limited monolayer coverage. Because bonds formed are chemical in nature, desorption often requires significant energy, making the process effectively irreversible under the original conditions. Physisorption, in contrast, is generally reversible and exothermic with low heats of adsorption and multilayer potential.

Step-by-Step Solution:
Differentiate by bonding: chemical vs. Van der Waals.Relate bonding strength to reversibility: strong bonding implies practical irreversibility.Select the option aligning with chemisorption: an irreversible phenomenon.

Verification / Alternative check:
Catalysis literature shows adsorbed intermediates bound strongly to active sites; desorption often requires higher temperature or reaction, consistent with practical irreversibility.

Why Other Options Are Wrong:

• Same as Van der Waals: Incorrect; that describes physisorption.
• “Adsorption of heat (endothermic)”: Adsorption is typically exothermic; wording here is misleading.
• Reversible: Describes physisorption more closely.
• No activation energy: Chemisorption often shows activation energy.

Common Pitfalls:
Assuming all adsorption is easily reversible; in chemisorption, strong bonding dominates behavior and kinetics.

Final Answer:
an irreversible phenomenon.