The diagram shows the fastest particles leaving the surface of a liquid during evaporation. The average kinetic energy of the particles left behind
Question 1 Report
The diagram shows the fastest particles leaving the surface of a liquid during evaporation. 
The average kinetic energy of the particles left behind
Answer Details
As shown in the diagram, evaporation occurs when the fastest particles at the surface of a liquid escape into the air. These escaping particles carry away more than the average amount of kinetic energy.
When the most energetic particles leave, the particles that remain behind have a lower average kinetic energy than before. Since temperature is a measure of the average kinetic energy of the particles, a lower average kinetic energy means a lower temperature. The liquid therefore cools down.
This is why evaporation is a cooling process. It is the basis for sweating in humans: as perspiration evaporates from the skin, the most energetic water molecules escape, taking energy with them and lowering the skin temperature.
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