Why is adsorption always exothermic ?

Explanation

### Step-by-Step Solution:

1. **Definition of Adsorption**:
- Adsorption is a surface phenomenon where molecules from a gas, liquid, or dissolved solid adhere to the surface of a solid or liquid. This results in a higher concentration of molecules at the surface compared to the bulk.

2. **Understanding Surface Energy**:
- When adsorption occurs, the molecules that adhere to the surface experience a change in energy. The energy associated with the surface is known as surface energy.

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