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After a hot sunny day, people sprinkle water on the roof-top because:
[UPSC CDS I 2016]
1) water helps air around the roof-top to absorb the heat instantly
2) water has lower specific heat capacity
3) water is easily available
4) water has large latent heat of vaporisation.
4) water has large latent heat of vaporisation.
What is latent (hidden) heat of vaporization ?
When a material in liquid state is given energy, it changes its phase from liquid to vapour without change in temperature, the energy absorbed in the process is called latent heat of vaporization.
Examples-
Ice absorbs a large quantity of latent heat during the process of melting.
Extinguishing fire by using boiling water
Water that is quickly boiled will become steam which is able to absorb a larger quantity of latent heat from the fire.
Melting Ice on the road by using Salt
The specific latent heat of fusion of salt is higher than of ice. Therefore, when salt is put on the road – having a thick layer of ice, salt will require more heat energy and absorb energy from the ice. Therefore, Ice will melt.
How Water has a high heat of vaporization?
Because hydrogen bonds form readily between the oxygen of one molecule and the hydrogens of other molecules. (H-O-H bond)
These bonds hold the molecules together. To get water to vaporize, we must increase the temperature to make the molecules move faster.