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.
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 EvaporationSurface 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 EvaporationTemperature
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
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, 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 EvaporationWind Speed
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 will 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.
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.
This was all about evaporation and condensation, if you are looking for detailed study notes on other topics of Class IX Chemistry then register yourself on Vedantu or download Vedantu Learning App for Class 6-10, IIT-JEE and NEET. By doing so you will get access to free pdfs of NCERT Solutions, Study Materials, Revision Notes and Mock Tests etc.