Question

We know that water changes into vapour when heated. But it is a common experience that water from wet roads, rooftops and floors disappears without heating. Explain how water changes into its vapour even without heating?

Answer 1

We all know that boiling point of water is 100°C. But what only few of us know is that, it is 100°C at pressure of 1 atmosphere (1.013 Bar).

So we can term it in two ways :

a) Saturation temperature corresponding to 1 atmosphere pressure is 100°C.

Or

b) Saturation pressure corresponding to 100°C is 1.013 bar

So at every pressure there is a critical temperature at which water starts to boil and at every temperature there is a critical pressure at which water starts to boil.

So whatever be your temperature you need to bring the pressure at the critical (Saturation) pressure corresponding to that temperature , and your water starts to boil.