# What condition applies when water boils at 100 C?

##### 1 Answer
Sep 1, 2016

An ambient pressure of $1$ $a t m$.

#### Explanation:

By definition, the boiling point of a substance is the temperature when the vapour pressure is equal to the ambient pressure, and bubbles of vapour form directly in the liquid. The normal boiling point is specified when the ambient pressure is $1$ $a t m$.

And thus we know, at $100$ ""^@C, water has a vapour pressure of $1 \cdot a t m .$