Why is chemical adsorption unimolecular while physical adsorption is multimolecular?

Explanation

**Step-by-Step Solution:**

1. **Definition of Chemical Adsorption:**
- Chemical adsorption, also known as chemisorption, involves a chemical reaction between the adsorbate (the substance being adsorbed) and the adsorbent (the surface on which adsorption occurs). This process results in the formation of a chemical bond.

2. **Unimolecular Nature of Chemical Adsorption:**
- Since chemical adsorption involves a reaction that leads to the formation of a stable bond, once a layer of adsorbate molecules is adsorbed onto the adsorbent, no further adsorption can occur at that site. This means that each site on the adsorbent can only hold one molecule of the adsorbate, making the process unimolecular.

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