Adsorption energetics:\nFor physical adsorption dominated by van der Waals attraction and capillarity, the heat of adsorption is approximately equal to the heat of ________.

Introduction / Context:
Physical adsorption (physisorption) involves weak interactions akin to condensation and additional energy effects when liquids wet solid surfaces or when capillary condensation occurs in pores. Understanding the energetic components clarifies why heats of adsorption are modest (compared to chemisorption) yet often exceed the latent heat of simple condensation alone on porous solids.

Given Data / Assumptions:

• Adsorption is physical (no chemical bonding).
• Surface is porous, allowing capillary condensation/wetting.
• Van der Waals attractions dominate.

Concept / Approach:
The total heat released during physisorption can be considered as the heat of liquefaction (condensation) of the adsorbate plus the heat of wetting of the solid by the adsorbate. The wetting term accounts for energy released when a liquid film forms on a solid, especially significant in porous materials where capillarity enhances adsorption at relative pressures below saturation.

Step-by-Step Solution:
Decompose energy: adsorption ≈ condensation component + wetting component.Recognize capillary action increases effective condensation in pores.Hence, the heat equals the sum of normal condensation and wetting.

Verification / Alternative check:
Calorimetric adsorption measurements often show heats slightly above the pure latent heat, consistent with an added wetting contribution.

Why Other Options Are Wrong:
Condensation alone underestimates porous-surface effects; wetting alone ignores phase change enthalpy; difference is not physical; sublimation is unrelated here.

Common Pitfalls:
Confusing chemisorption (much higher heats due to bond formation) with physisorption.

Final Answer:
sum of (a) and (b)