Wikipedia says that a substance that has a larger surface area will evaporate faster, as there are more surface molecules that are able to escape. I think the rate of evaporation should decrease as there are more surface molecules. I want to know that what is the surface area of a liquid? And also that why the rate of evaporation increases with increase in surface area of the liquid?
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The surface of a liquid is the interface between the liquid and (usually) the air surrounding it. The surface area is the amount of that liquid that is exposed to the air, or touching the air.
If more liquid is exposed to the air, then more of it can evaporate.
To be particular, depending on how you define rate of evaporation, you could say that it stays constant not depending on the surface area. However, with more of the liquid exposed, there is more liquid evaporating at a time (at the given rate $\frac{V}{A\cdot t}$). |
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Because in a liquid, the molecules are all about the same distance apart (since most liquids are not very compressible). So the top surface of liquid in your coffee cup has a certain area and a certain number of molecules in that area. Two cups of coffee will have twice as much area, so twice as many molecules, so twice as much evaporation. Now connect the two cups by a narrow tube below the surface. What you have then is a single quantity of liquid with twice as much surface area as one cup, and, of course, twice as much evaporation. |
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The surface area affects evaporation because if more area is exposed to air, allowing water molecules acquire more heat energy from the surroundings. Due to the increased heat energy (kinetic energy), there is more rapid movement of the water molecules which helps them to overcome the force of attraction and evaporate. The progression is essentially more area -> more heat absorption -> increased kinetic energy -> increased movement -> faster evaporation. |
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