Evaporation requires the removal of heat?

In summary, the conversation discusses the concept of evaporation and its relationship to heat. The experts explain that water needs heat to evaporate, but the heat is not used to increase the water's temperature. Instead, it is used to free the water molecules, a process known as latent heat. The surroundings then become cooler as the water molecules escape into the atmosphere. Boiling water helps speed up the evaporation process, but it can still occur at room temperature. The experts also mention personal experiences with evaporation, such as sweating to cool down. The conversation concludes with the acknowledgement of mpv_plate's explanation as the desired answer.
  • #1
I'm missing out on something here.

I'm studying how the cooling tower works and it says that the "water evaporates and removes heat". The thing is, shouldn't the heat be added to the water for it to evaporate and thus increasing the heat? If we want water to evaporate, we boil it with fire, which is once again heat addition.

Care to clarify this for me?
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  • #2
Water needs heat to evaporate, but the heat does not increase temperature of water: the heat is used to free the water molecules. It is called the latent heat. Water gets this latent heat from the sorrounding material, so the sorroundings get cooler.
  • #3
We boil it so that the water is hotter than the air and then it evaporates quickly. If we don't boil it then it will be room temperature, and it will still evaporate. This is because water has many molecules in it and some are more energetic than others. The "hotter" (more energetic) molecules and bits of water have enough momentum to escape the liquid and go into the atmosphere. This leaves the liquid cooler because the hot molecules have escaped. This should jive with your personal experience. If we boil water it cools down as it evaporates, the hot water is leaving. If you sweat you cool down because the hot water molecules on your body leave and what is left are colder molecules.
  • #4
Thanks to both of you but the answer I was looking for was answered by mpv_plate. Appreciated!

1. What is evaporation?

Evaporation is the process by which a liquid turns into a vapor or gas. This occurs when the molecules of a liquid gain enough energy to break free from the surface and enter the gas phase.

2. Why does evaporation require the removal of heat?

In order to turn from a liquid to a gas, the particles of the liquid must gain energy and overcome the attractive forces holding them together. This energy is obtained by absorbing heat from the surroundings, which lowers the temperature of the remaining liquid.

3. What happens to the temperature of a liquid during evaporation?

The temperature of a liquid decreases during evaporation, as the molecules with the highest energy are the first ones to escape into the gas phase. This results in a decrease in the average kinetic energy of the remaining molecules, leading to a lower temperature.

4. What are some factors that affect the rate of evaporation?

The rate of evaporation can be affected by several factors, including temperature, humidity, surface area, and air flow. Higher temperatures and lower humidity levels typically result in faster evaporation, while a larger surface area and increased air flow can also speed up the process.

5. Is evaporation a physical or chemical change?

Evaporation is a physical change, as it does not involve a change in the chemical composition of the substance. The liquid molecules are simply changing state from a liquid to a gas, but the substance itself remains the same.

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