why is evaporation called a surface phenomena

Surface phenomenon is the phenomenon where only surface of any substance or object is involved in the process. On the other hand, bulk phenomenon refers to the phenomenon where whole of the substance or object is involved in the process and is affected in bulk completely. In evaporation, only the molecules of the liquid present on the surface of the liquid leave the liquid state and change into vapour state. It does not affect the molecules present in the bulk of the liquid. Thus, evaporation is a surface phenomena. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out. 

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