How does evaporation cause cooling?
Each molecule in the liquid phase is attracted to the other molecules in the liquid. When a molecule changes phase ( evaporates) it has to break all those intermolecular forces so it can escape. Only the molecules that have sufficient kinetic energy can do this. These high energy molecules leave to the gas phase and the remaining molecules are the ones that did not have enough energy to evaporate. This, the average kinetic energy of the molecules in the liquid left behind is lower that it was before the hot ones leave. So, evaporation “cools” what is left behind because the heat was used up breaking the hotter molecules out into the gas phase.On a hot day you sweat. That sweat evaporates and carries away heat. Your body gave that heat to the sweat ( water) so your body cooled off. This is important as a means by which your body can avoid overheating.
Why does a liquid having less boiling point show cooling affect faster?
All other conditions being same, the liquid with less boiling point would evaporate faster at the given temperature and since the heat of evaporation is taken from the liquid, the cooling effect is faster.Example - spirit rubbed on the skin (before giving an injection for example) gives a cooling sensation almost immediately unlike water.
How is evaporation different from boiling? Does water reach 100C when it evaporates? If yes, how does evaporative cooling decrease air temperature? In what direction does heat transfer take place?
Evaporation occurs whenever a molecule of the fluid leaves the surface and is able to escape the intermolecular forces of attraction. Boiling just increases the rate of evaporation.In any fluid, most molecules have some average speed, some have very low speed and some have very high speed. Evaporation occurs when some high speed molecule, which has enough speed to overcome intermolecular forces of attraction, escapes from the fluid into air.At high temperatures, evaporation increases because more molecules have enough energy to escape.Also, air should be dry. Air can only carry a limited amount of moisture and once it is reached, water won’t evaporate anymore.I have given few more details hereAt room temperature, water isn’t boiling. Then why does it evaporate?And a short article on evaporative cooling hereHow will you cool something ?
What is the relationship between boiling points and intermolecular forces?
The stronger an intermolecular force, the higher the boiling point of the substance will be , because stronger intermolecular bonds require more energy to break and this energy is supplied in the form of heat when boiling, substances with stronger bonds will have a higher boiling point.Typically, more the pressure will be , the higher the boiling point will be . We can take here water as an example. At sea level, 14.7 psi is the atmospheric pressure and the boiling point of water is about 100°C.Where as At 14,000 feet,8.6 psi is the air pressure and the boiling point is about 86 °C. Therefore in the mountains, it takes longer to boil an egg than when you're at sea level. A device using relationship between boiling point & pressure is a pressure cooker.
How does evaporation cause cooling?
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
The cooling effect inside a refrigerator is produced by?
b. Vaporizing the refrigerant liquid. The reason is the hot temperature is TAKEN OUT by low boiling temperature of the refrigerant. Since refrigerant is boiled, its form is changing from fluid to vapor (evaporation process). Since hot temperature is taken away, the cooling effect is occured.
Why is ice at 273 Kelvin more effective in cooling than water at the same temperature?
Ice at 273 K will absorb heat energy or latent heat from the medium to overcome the fusion to become water. Hence the cooling effect of ice is more than the water at same temperature because water does not absorb this extra heat from the medium.It is clearly written in the class 9 NCERT science book. If you want you can request me any chapter and I will teach you that chapter.Here is my blog link gien below:-9SIMPLYSCIENCEThanks.