Adsorption and Catalysis

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Adsorption is the phenomenon where molecules of a gas or solute are attracted and retained on the surface of a solid, leading to higher concentration on the surface. Example: Silica gel adsorbs water …

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Adsorption is surface retention of molecules (e.g., water on silica gel), while absorption is uniform distribution throughout the bulk (e.g., water absorbed by calcium chloride).

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Powdered charcoal has a larger surface area due to smaller particle size, providing more sites for adsorption. Greater surface area increases adsorption capacity.

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Easily liquefiable gases have stronger intermolecular forces (van der Waals), making them interact more strongly with the adsorbent surface, leading to higher adsorption.

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Physical adsorption decreases with increase in temperature because it is exothermic. According to Le Chatelier’s principle, low temperature favors the forward process (adsorption).

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At constant temperature, increasing pressure increases the extent of adsorption as more gas molecules are forced onto the surface until saturation is reached.

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The enthalpy of adsorption for physical adsorption is low, typically between 10–40 kJ/mol, due to weak van der Waals forces.

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The enthalpy of adsorption for chemisorption is high, ranging from 40–400 kJ/mol, due to the formation of chemical bonds between adsorbate and adsorbent.