[Chemistry Class Notes] on Evaporation and Condensation Pdf for Exam

Take a beaker and put water in it. Now put this beaker on the flame and keep heating it. After some time, you will notice that water starts boiling and changes into vapor. This phenomenon is called vaporization. Now have you noticed that if a glass of water falls on the floor and no one wipes it but still after some time it dries. In the same way wet clothes dry up after some time. Do you know how? Well as we know that particles of matter are always moving and are never at rest it means they possess different amounts of kinetic energy at different temperatures. In the case of liquid as well a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapors. This phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.

 

Factors Affecting Evaporation

Following factors affect rate of evaporation –

• Surface Area – Evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation also increases. For example, we spread clothes out to dry them faster. Relation between rate of evaporation and surface area can be written as –

 

Rate of Evaporation α Surface Area

• Temperature – Rate of evaporation increases at higher temperatures. As with increase of temperature, a greater number of particles get enough kinetic energy to go into the vapor state. For example, wet clothes dry quickly under sunlight. Relation between rate of evaporation and temperature can be written as –

 

Rate of Evaporation α Temperature 

• Humidity – Humidity is the amount of water vapor present in air. Air cannot hold more than a definite amount of water vapor at a given temperature. If the amount of water in air is already high or maximum, the rate of evaporation decreases. Relation between rate of evaporation and surface area can be written as –

 

Rate of Evaporation α [frac{1}{Humidity}]

 

• Wind Speed – With increase in wind speed, the particles of water vapor move away with the wind, decreasing the amount of water vapor in the surrounding. Thus, an increase in wind speed increases the rate of evaporation as well. For example, clothes dry faster on a windy day. Relation between rate of evaporation and surface area can be written as –

 

 Rate of Evaporation α Wind Speed 

What is Condensation?

Again, take a beaker and put water in it. Now put this beaker on the flame and keep heating it. After some time, you will notice that water starts boiling and changes into vapor. Now cover the beaker with a lid and stop giving it heat. After a minute when you take out the lid you will see water droplets on one side of the lid. This is because water vapor gets condensed and changes into liquid again. Condensation is the change of the physical state of matter from gas phase into liquid phase. This is a reverse phenomenon of vaporization. 

When you take out a chilled soft drink bottle from the fridge and keep it aside after drinking then after some time you notice small drops of liquid on the surface of the bottle. This is also an example of condensation. It takes place when the vapor in the warm air meets a cool surface and cools down to change its state.

 

Reason Behind Condensation Process 

Like other matters, water also consists of atoms. These atoms are energetic so move rapidly. These particles are far from each other when they are in the form of vapor. So, when this vapor comes in contact with cooler temperatures, particles become less energetic and come closer to each other. Thus, vapor changes into liquid upon reaching threshold energy level.

 

Difference Between Evaporation and Condensation

What is the Water Cycle?

The continuous processes of evaporation and condensation are cyclic, that is they occur simultaneously creating the water cycle. Water cycle is a complex system that shows the movement of water through the Earth and its atmosphere in different forms- liquid and gas. Evaporation and condensation are the most important processes in the water cycle. It is through evaporation that the surface water rises up in the atmosphere in the form of water vapor and through condensation that it transforms into clouds which eventually brings rain.

Uses and Application of Evaporation

A traditional way to produce table salt that is still applicable in many parts of the world is through the process of evaporation. If you fill a bowl with sea water and keep it at an open temperature, the water will evaporate through the sun’s heat leaving behind fresh salt. Evaporation ponds work with the same mechanism; large amounts of saline water is dried through evaporation in these ponds to extract table salt, magnesium, potash and bromine.

As mentioned earlier, through the process of evaporation heat is removed from the atmosphere. This property of evaporation is used exclusively in evaporators and swamp coolers. Evaporators are massive machines used in industries to vaporize compressed cooling chemicals to remove excessive heat. Alternatively, in other industries it can be used to separate various compounds like water from crude oil. They are also used to not only concentrate food and dairy products but also to remove moisture from drugs produced in pharmaceutical industries.

Similarly, swamp coolers or evaporative coolers are used in countries of hot temperatures to lower the air temperature and provide some relief.

 

Uses and Application of Condensation

The process of distillation follows the process of condensation, which is essential for separating different substances from mixt
ures in laboratories and industries. Condenser is the device that is used to condense vapor. Condensers are used in air conditioners or heat pumps to either collect or release heat as per the requirement. In industries, it is used in various heat exchange systems and steam power plants.

As we know, condensation is the phenomenon through which water is produced in the liquid form; that is why many structures are built- like dew wells and fog fences-  that work on this process to collect large amounts of liquid water for domestic use, agricultural use and industrial use in places of high desertification or no nearby water body.