Whenever energy is supplied to or taken out of matter, It always brings about one or the other kind of change.
Taking examples from our daily life- The heat energy of the sun causes the evaporation of water. The water vapors on losing heat energy at higher altitudes change to cloud snow.
When an electric current is passed through an electric bulb, its filament glows. The milk sours quickly if not kept at a low temperature. The wood on burning produces a large amount of heat and leaves ash behind. Food taken by us changes into carbon dioxide and other materials producing heat.
All these changes take place with an impact of temperature.
From the above examples, it is clear that some kind of change always takes place in the matter, when subjected to energy changes. Almost all the changes (except nuclear changes) taking place in a matter can be classified under two headings, i.e., 1. Physical Changes. 2. Chemical Changes.
In the process of evaporation, the change happens which alters some specific physical property of the matter, like its state, texture, etc conditions or its colour, without any change in the composition of its molecules, provided it gets reversed, if the cause producing the change is removed.
Is Evaporation Endothermic Or Exothermic? Evaporation is basically an endothermic process in which liquid particles change their state to gaseous form even below the boiling point.
Why The Evaporation Process Is Endothermic?
The heat energy which is supplied to the particles is also known as kinetic energy.
As we know, Evaporation takes place only if liquid particles gain a greater amount of heat. And you know acquiring heat is an endothermic process.
Some of the particles even below the boiling point have greater kinetic energy than that of other ones.
This kinetic energy is substantial to overcome the force of attraction between the particles of the liquid. This helps to break down the intermolecular forces that exist among particles. Therefore, particles escape from the liquid surface in the form of gas.
The process of evaporation does not take place in intervals but is continuous in which the particles following the endothermic process gaining heat turns into vapor form and escape from the surface of a liquid.
There are several factors that impact the endothermic evaporation process:
- Surface area
- Wind speed
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No new or different product
The composition of molecules of the substance remains unaltered. Just like, Ice melts to form water. Only the appearance (state) of matter has changed from solid to liquid. The composition of the molecules of ice or water remains the same, i.e., for every 1 g of hydrogen, there is 8 g of oxygen. These all factors also remain in evaporation when changing from liquid to vapors. Thus, an endothermic evaporation change occurs.
Temporary and reversible
It means the change can be reversed by altering the causes which produce the change. No substance is formed when changing its state. This is similar to water formed from ice can be changed back to the ice by placing it in a freezing mixture (a mixture of ice and common salt). Thus, on altering the experimental conditions, the change which gets reversed is a physical change.
no gain or loss of energy
The amount of energy required to bring about an endothermic change is generally equal to the amount of energy required to reverse the change. Thus, there is no energy change involved. If 1 g of water at 100 °C on changing into steam needs 2260 J of heat energy, then 1 g of steam at 100 °C on changing into the water at 100 °C, gives out 2260 J of heat energy. Thus, the net energy change is zero.
No change in Weight
There is no change in the weight substance. During the evaporation change, it is the only energy that is added or removed. If 1 g of water at 100 °C on steam needs 2260 J of heat energy, changing into steam needs 2260 J of h then 1 g of steam at 100 °C on changing or Cat 100 °C, gives out 2260 J of heat energy. Thus the net energy change is zero.
The mass of the substance in endothermic change remains the same. No matter is added during a physical change. similarly, no matter is removed during a physical change. Therefore, the mass of the substance remains same.
is evaporation of water endothermic or exothermic
We all know that In liquids, the intermolecular force of attraction is enough to keep the molecules in contact with each other. Hence, the molecules of water are free to move within the body of the water. Therefore they can easily take the shape of a container.
When we expose water to air, it is a natural tendency that the volume starts to decrease. This is all because of evaporation. The liquid particles turn themselves into vapors and this happening is said as evaporation. It is to remember the process of evaporation even takes place below boiling point. As we increase the temperature of the liquid, the process of evaporation after gaining heat from an external source becomes faster. So, the evaporation of water is an endothermic process.
Evaporation of liquid takes place also at room temperature. More heat we see in summers, quicker evaporation process takes place whereas in winters the process slows down.
After understanding water behaves as endothermic to attain the state to evaporation, it is good to discuss What happens after the evaporation.
- The molecules in water vapours are far apart from each other.
- The intermolecular space is maximum.
- The intermolecular force of attraction is minimum or negligible.
- The water vapours have neither definite shape nor definite volume.
- Beacuse of evaporation, water vapours flow easily in all directions.
- water vapours have minimum density.
- water vapours have maximum compressibility. As the intermolecular space is maximum. So, on applying pressure, the molecules come closer to each other.
- steam vapours do not have any free surface.
- After water evaporation rapidly undergo the process of diffusion. It is the process of intermixing of gases without applying any external agency so as to form homogeneous mixture.
- When heated or cooled vapours show appreciable expansion or contraction. The intermolecular space in gases is maximum, therefore the molecules do not feel the appreciable force of attraction.
Moreover, the molecules have maximum kinetic energy. So the molecules move freely practically in all directions filling all the spaces. Thus, they have neither definite volume nor definite shape. The phenomenon of the conversion of matter from its one state to another and back to its original state by changing the conditions like temperature and pressure etc. is called interconversion of matter.
Earthen Pot: In the earlier times, when there was no refrigerator, no cooling techniques to cool down the water. The earthen pot was used. It is made of mud and has small little pores that significantly decrease the temperature of the water. The small pores allow minute particles to escape by taking away the heat from the water thus cool down.
Evaporation of sweat endothermic or exothermic: When our body feels hot or we sweat on a hot day or do some physical exercise. Our body temperature rises. Our skin small pose gives out a sweat on the skin. When this sweat following the endothermic process evaporates we feel cool. This happens because the minute particles on our skin grasp the body heat turns themselves into vapors form and evaporates. They take away our body heat thus we feel cold.
The evaporation process can be initiated with the endothermic (absorbance of heat). The temperature required varies with the molecular structure of the substance. Some liquids are more viscous and need more heat to reduce their viscosity. More viscosity means the greater force of attraction among particles of the liquid. This tends to take a greater amount of heat that is a part of the endothermic process. So, massive heat is required to excite the small particles to break down the bonds or attraction and turn them into a gaseous state.
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