* When wet cloths are drying you noticed that water in the wet cloths disappears,
where dose the water go ?
*When the floor of a room washed with water,the water on the floor disappears within a few minutes and floor become dry,
Why dose water on the floor disappear after some time?
Evaporation
To understand Evaporation we have to do an activity with spirit.
1) take a few drops of spirit in two petri dishes separately.Keep one of the dishes containing spirit under a ceiling fan and switch on the fan.
2) Keep another dish with its lid closed. Observe the quantity of spirit in both the dishes after 5 minutes.
* what we notice?
3) we will noticed that spirit in the dish that is kept under the fan disappears,where as we will find out that some spirit in the dish that kept in the lidded dish.
https://youtu.be/kXHFRSwIiQ4
* what could be the reason for this change?
To answer this equation we must understand the process of EVAPORATION.
4) The molecules of spirit that is kept in petri dish,continuously moves with random speeds in different directions.As a result these molecules collide with other molecules.
5) During that collision they transfer energy to other molecules.
When the molecules inside the liquid collide with molecules at the surface,the molecules at the surface acquire energy and may fly off from the surface.
6) Some of these escaping molecules may be directed back into liquid when they collide with the particles of air,
7) if the number of escaping molecules is greater than the number returned,then the number of molecules in the liquid decreases.
8) Thus when a liquid is exposed to air,molecules at the surface keep on escaping from the surface till the entire liquid disappears into air.this process is called Evaporation.
9) During the process of evaporation,the energy of the molecules inside the liquid decreases and they slow down. They transfer this energy to escaping molecules during the collisions,
” The process of escaping of molecules from the surface of a liquid at any temperature is called Evaporation”
reason for faster evaporation of spirit keep under the fan
If air is blown over the liquid surface in an open petri dish,the number of molecules returned is reduced to a large extent.This is because any molecule escaping from the surface is blown away from the vicinity of the liquid.This increase the rate of evaporation.This is the reason why the spirit in petri dish that kept under the fan evaporates quickly when compared to that kept closed.
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