The Langmuir adsorption model assumes adsorption sites are ...

The Langmuir adsorption model assumes adsorption sites are ...

• A. Heterogeneous with variable energy
• B. Capable of multilayer stacking
• C. Dependent on adsorbate-adsorbate interactions
• D. Energetically equivalent and independent

Answer: (D)

The Langmuir model rests on the idea that adsorption occurs on a finite set of identical sites, and each site can hold at most one molecule. All sites have the same energy of adsorption, and placing a molecule on one site does not affect neighboring sites—the adsorbates do not interact laterally. This combination leads to a simple monolayer scenario where surface coverage depends only on the gas-phase pressure and the adsorption–desorption equilibrium. If the surface had sites with different energies, you’d expect a distribution of binding strengths and different isotherm behavior (not the uniform, single-energy picture). If multilayer stacking were possible, the model would need to account for additional layers beyond the first. If adsorbate–adsorbate interactions were significant, the occupancy of one site would influence others, again deviating from the Langmuir assumptions.

The Langmuir model rests on the idea that adsorption occurs on a finite set of identical sites, and each site can hold at most one molecule. All sites have the same energy of adsorption, and placing a molecule on one site does not affect neighboring sites—the adsorbates do not interact laterally. This combination leads to a simple monolayer scenario where surface coverage depends only on the gas-phase pressure and the adsorption–desorption equilibrium.

If the surface had sites with different energies, you’d expect a distribution of binding strengths and different isotherm behavior (not the uniform, single-energy picture). If multilayer stacking were possible, the model would need to account for additional layers beyond the first. If adsorbate–adsorbate interactions were significant, the occupancy of one site would influence others, again deviating from the Langmuir assumptions.