Evaporation is a cooling process. What cools and what warms?

In summary, evaporation is a process by which water molecules lose energy and become part of the gas phase. This reduces the temperature of the substance, and in the case of evaporation, it also reduces the temperature of the air around the substance.
  • #1
Gc2012
2
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Evaporation is a cooling process. What cools and what warms? Also, condensation is a war,ng process. What cools and what warms?

I understand that during evaporation the water molecules of water slow down therefore cooling down. But does this mean that the air warms up? The opposite goes for condensation, the object upon which the vapor condenses is warmed. So whatt's cooled? The air vapors?

Thanks.
 
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  • #2


Evaporation means that molecules of the liquid leave the liquid phase and become part of the gas phase above the liquid. Only those molecules can escape from the liquid which have enough energy. You know that the temperature of the substance is proportional to the average KE of its molecules. Loosing molecules with high energy would decrease the average energy of the remaining molecules, so the liquid losses heat when evaporating. The energy of the escaped molecules is transferred as heat to the gas phase above the liquid. ehild
 
  • #3


Gc2012 said:
Evaporation is a cooling process. What cools and what warms? Also, condensation is a war,ng process. What cools and what warms?

I understand that during evaporation the water molecules of water slow down therefore cooling down. But does this mean that the air warms up? The opposite goes for condensation, the object upon which the vapor condenses is warmed. So whatt's cooled? The air vapors?

Thanks.

The temperature of water is a measure of the average kinetic energy of the particles.
In any sample of water, some molecules will have above average energy, others below average.
If a water molecule is lucky to have enough energy, it can exist as a gas molecule, rather than just part of the liquid. If it happens to be near the surface, it may even escape the liquid. If there is a breeze blowing, it may get swept away, while still a gas molecule, and thus not return, with its energy, to the body of liquid.

Note that this means one of the more energetic molecules in the original sample has left with its energy, meaning the average energy of the molecules left behind is lower - the water is cooler [remember temperature is a measure of the average KE of the particles.

Imagine doing this with money in a group of people. The average wealth of a group of 20 people is $1000. People exchange amounts of money between them selves - but the average wealth remains the same. Suddenly, one person notices that they are currently holding $5000, so decides to leave the group and take that money with them.
The remaining 19 people now have a collective wealth of $15000, so an average wealth of of just under $790. The average wealth of the group reduced when one member of the group evaporated.


We could cover condensation in the same way.
The average energy of the water molecules is sufficient for them to be a gas. Some have high energy, some have low energy, but the average is what ever it is.

At some time, there may be a group of atoms which individually only have sufficient energy to be a liquid, so they fall to the bottom of the container as a water droplet. The average energyof the remaining water molecules in the gas is now higher ... ... etc.
 
  • #4


It all makes perfect sense now.

This is the first time I post anything on any forum (I know weird), but the replies you gave were great! Thank you again.
 
  • #5


I can explain that evaporation is a cooling process because when water molecules have enough energy, they break free from the liquid and become water vapor. This process requires energy, which is taken from the surrounding environment, resulting in a decrease in temperature. Therefore, the water itself is cooling down as it loses energy to become water vapor.

On the other hand, during condensation, water vapor molecules lose energy and come together to form liquid water. This release of energy warms up the surrounding environment. So in this case, the water vapor is cooling down, while the air or object that the water vapor condenses on is being warmed.

It's important to note that the overall temperature change during evaporation and condensation depends on the amount of energy exchanged between the water and the surrounding environment. In some cases, the air may become slightly warmer during evaporation, while in others it may remain the same or even cool down. Similarly, the object that the water vapor condenses on may not necessarily warm up, as it also depends on the amount of energy exchanged.

In conclusion, evaporation and condensation are both processes where energy is exchanged between water and the surrounding environment, resulting in changes in temperature. The specifics of what cools and what warms may vary depending on the situation, but the overall process remains the same.
 

1. How does evaporation cool the environment?

When a liquid evaporates, its molecules gain energy and transform into a gas. This process requires heat, which is taken from the environment. As a result, the surrounding area becomes cooler.

2. What cools faster, hot water or cold water?

Hot water cools faster than cold water because the molecules in hot water have more energy and can evaporate more quickly. This means that hot water loses heat at a faster rate compared to cold water.

3. Does humidity affect the cooling effect of evaporation?

Yes, humidity can affect the cooling effect of evaporation. When the air is already saturated with water vapor, there is less room for evaporation to occur. This means that the cooling effect of evaporation is reduced in humid environments.

4. What role does surface area play in evaporation?

The larger the surface area of the liquid, the more molecules can escape through evaporation. This means that a larger surface area can result in a faster rate of cooling through evaporation.

5. How does wind affect evaporation as a cooling process?

Wind can increase the rate of evaporation by blowing away the water vapor around the liquid, allowing for more molecules to escape into the surrounding air. This results in a faster cooling effect compared to still air.

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