[shalikadm]

We have learned that the temperature of a liquid doesn't rise when it undergoes a phase shift though we're supplying heat. For and example the temperature of water and water vapour will be 100°C until the whole liquid becomes gas. Then only after that its temperature rises.
It will be the same for vapour preasure ?
Will it remain constant (1 atm) till the whole water becomes water vapour in its phase shift (change) ?

[Borek]

You need to keep the pressure constant for the boiling temperature to stay constant. In typical situation (boiling in a open vessel) pressure is constant, so you don't have to worry. If you will try to heat water in a closed vessel, situation becomes much more complicated.

[shalikadm]

If you will try to heat water in a closed vessel, situation becomes much more complicated.

I too feel it. When it is in a closed vessel the pressure will rise and would make an influence on vaporizing. But why my book has defined boling point as the following ?,

The standard boiling point of a pure liquid is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid when heating in enclosed vessel

But I don't find that closed vessel thing in Wikipedia

The boiling point of a substance is the temperate at which the vapor pressure of theliquid equals the pressure surrounding the liquid[1][2] and the liquid changes into a vapor.

Now just take an open vessel.... Will the vapour preasure be constant while its on the phase shift and get increased after the whole liquid is vapourised ? Or just constant along ?

In typical situation (boiling in a open vessel) pressure is constant, so you don't have to worry.

[Borek]

If you heat something in a closed vessel, the pressure will change with the temperature. When we determine the boiling point we want to know exactly what the pressure is, so we do it in an open vessel so that the pressure is constant and equal to the atmospheric pressure during experiment.

Boiling point definition doesn't ask for open or closed vessel, it requires a known and constant pressure (doesn't matter how you achieve this, although using an open vessel and atmospheric pressure is the simplest approach).