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I know the equations, but I have some difficulty getting the difference between the two concepts of binding energy and adsorption energy.

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For solids, the binding energy is what makes the crystal (if you will) hold together. It is what makes the individual constituents of the compound bind together.

Adsorption however is an entirely different process: Here, some molecules interact with the surface of another compound. Since (strictly speaking) this is no chemistry but mere physics (there is no formation or breaking of bonds) there are other interactions at play, mainly van der Waals-type interactions.

As these are weaker (it's easier to wipe off the water from your windshield than rip out a silicon atom) and aren't based on the same principles as the binding energy, they get a different name.

I hope that cleared things up for you.

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    $\begingroup$ Chemisorption is adsorption where an actual covalent bond is formed. Just to throw that out there. $\endgroup$ – jheindel Nov 20 '15 at 18:13
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I have the same question. Though the answer from tschoppi is only partially correct. Chemists have divided adsorption processes on at least two classes: physisorbtion and chemisorbtion. The tschoppi's answer is relevant for physisorption, though it does not answers the question. Exampple of chemisorbtion: carbon monoxide on platinum. In this case CO is realy chemically bonded to top platinum atoms. The difference between the adsorbtion energy and the binding energy depends on the person you ask. It is a matter of definition. I would call binding energy is the enrgy of a chemical bond between a particular adsorbed molecule and a particlar atom of the surface. This energy should be weakly influence by the neightbouring adsorbates. However, adsorbate do interact. For strongly covered surface the energy required to pull out a molecul is less then for an almost clean surface. This energy, I believe, is the adsorbtion energy, which is coverage dependednt. At low coverages the adsorbtion energy and binding energy are the same. That is the difference is due to the intercation of adsorbates with each other.

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