how does evaporation cause cooling?

Question

I know that when we sweat the water molecules evaporate by absorbing energy and cool us down but does that means the molecules become cold after the energy absorbtion?Wont they get hot due to energy absorbtion?

Answer 1

When a liquid, say, water evaporates, it undergoes a phase change, in this case the water turns from liquid state to vapour state. For this phase change, it requires a certain amount of heat known as the "latent heat of evaporation". This heat is absorbed from the surface which gets cooled. The heat lost by the surface is called "specific heat". The important difference here is between latent heat and specific heat. The effect of latent heat is not felt as a temperature change, only a phase change,hence the name "latent", meaning hidden. The effect of specific heat , on the other hand is felt as a definite temperature change. This is why the water molecules do not get hot. They absorb energy, but this energy is used to change their state, and not increase their temperature, hence the temperature remains same

Answer 2

Evaporation is exclusively a surface phenomena and should not be confused with boiling. The thermal motion of a molecule of liquid must be sufficient to overcome the surface tension to evaporate, that is, its kinetic energy must exceed the work function of cohesion at the surface. Evaporation therefore, proceeds more quickly at higher temperature, at higher flow rates between the gaseous and liquid phase and in liquids with lower surface tension (i.e. higher vapor pressure). Since only a small proportion of the molecules are located near the surface and are moving in the proper direction to escape at any given instant, the rate of evaporation is limited. Also, as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also called evaporative cooling. This is why evaporating sweat cools the human body. Gas has less order than liquid or solid matter, and thus the entropy of the system is increased, which always requires energy input. This means that the enthalpy change for evaporation (ΔHevaporation) is always positive. Evaporation is a cooling process.

Answer 3

The Total sum of energy will decrease because
there is a loss of energy due to "water/sweat"(whith energy)
leaving the body.

The main body-mass is approx. the same and therefore bodytemperature must decrease. It means the kinetic energy
(velocity of moleculaer movements ) will become "slower"

The molecules themselves dont get cold , they just move faster
or slower, the faster - the more energy they get (hoter).

When the velocity of the "individual molecule" is above a limit,
it can leave the body and there is a loss of energy to the body.

After leaving the body the the molecule encounter a new story
depending what it meets.

Hope this adds to your understanding.

Answer 4

water molecules absorb the energy and then evaporate. it is like when you boil water.. the molecules have absorbed energy and start to move faster due to the heat. the fast moving molecules break away and the sweat evaporates. energy is needed to separate the particles of a liquid to form a gas

Answer 5

energy moves from surpluses to sinks, so some of the surplus of energy your body has that makes you feel hot is used by the water molecules to cause the process of evaporation. the use of that energy transfers energy from you to the water and evaporation process, thus leaving your body with less energy than it had before. this process recurring over and over all over your body, or wherever you are sweating leaves you with much less energy in your body and therefore you feel cooler. this process is called "latent heat of evaporation". its also partly why climates next to large bodies of water are more moderate than land-locked climates.

Answer 6

Evaporation effectively requires inputting of the latent heat of fusion into the molecule, which must be coming from the skin:
http://en.wikipedia.org/wiki/Evaporation#Entropy

Answer 7

Evapouration needs some amount of heat . Always remember that when any substance is getting evapourated then it takes heat mainly from itself & also from surrounding in small amount . Hence as a result the temperature of asubstance is reduced & substance gets cooled .

Answer 8

The sweat absorbs the heat from our skin. Have you ever felt sewat? It's hot.

Answer 9

the most energetic molecules leave your body so you wount feel that hot cause the hot ones have left. thats why it can occur at all temperatures...

Answer 10

It removes heat , just like why we sweat.