# Vapour pressure and boiling [duplicate]

I have come across two definitions for boiling point:

1. It is the temperature at which a liquid gets vaporised

2. It is the point where vapour pressure = external pressure

How are they related? How does vapour pressure being equal to external pressure cause a liquid to vaporise?

• Do you really think water on a wet floor boils, while the floor is getting dry ? Have you searched about terms "vapour pressure" and "boiling" ? // In contrary to some other Q/A or forum sites, answers on CH SE site are figuratively paid by the user's own effort. When you ask, it is expected you have thoroughly searched and thought about the topic, providing summary of partial answers/ideas you have got until then. Effort not shown may be considered as effort not done and such a question may get closed. How do I ask a good question. Commented Sep 13, 2021 at 12:09
• The first condition is incorrect and the 2nd condition is correct. To boil,, a liquid must form vapor bubbles beneath the surface, in the bulk of the liquid. These bubbles will contain pure vapor at the equilibrium vapor pressure. In order for these bubbles to form, the pressure inside the bubble must be high enough to expand the total volume liquid and bubble below the surface by pushing back the outside atmosphere. This can only happen if the pressure in the bubbles is equal to the outside atmosphere pressure. Commented Sep 13, 2021 at 16:07
• @Poutnik I know about vapour pressure, but these are the definitions given in the book I'm following, hence the question Commented Sep 14, 2021 at 10:39
• I have got it, but critical thinking is supposed to be applied on everything. What is written is not necessarily correct, and in this case it is easy to verify without asking. // Def 1 is also about wording evaporates versus gets vaporized ( the former anytime, the latter is the final stage of evaporation where temperature cannot get higher and heat is used for phase change ( for given p and neglecting metastability) Commented Sep 14, 2021 at 10:49