Editing Vapor (section)

==Vapor pressure==
{{Main|Vapor pressure}}
[[File:Binary Boiling Point Diagram new.svg|class=skin-invert-image|left|thumb|Liquid–vapor equilibrium]]
[[File:Vapor being used in a cloud chamber.jpg|thumb|If the [[vapor pressure]] exceeds the [[List of types of equilibrium|equilibrium]] value, it becomes [[supersaturated]] and [[condenses]] on any available [[nucleation]] sites e. g. [[particles]] of dust. This principle is used in [[cloud chamber]]s, where particles of [[radiation]] are visualized because they [[nucleate]] formation of water droplets.]]
The [[vapor pressure]] is the equilibrium pressure from a liquid or a solid at a specific temperature.  The equilibrium vapor pressure of a liquid or solid is not affected by the amount of contact with the liquid or solid interface.

The [[normal boiling point]] of a liquid is the [[temperature]] at which the vapor pressure is equal to [[atmosphere (unit)|normal atmospheric pressure]].<ref name=Petrucci/>

For two-phase systems (e.g., two liquid phases), the vapor pressure of the individual phases are equal.  In the absence of stronger inter-species attractions between like-like or like-unlike molecules, the vapor pressure follows [[Raoult's law]], which states that the [[partial pressure]] of each component is the product of the vapor pressure of the pure component and its mole fraction in the mixture. The total vapor pressure is the sum of the component partial pressures.<ref>Thomas Engel and Philip Reid, ''Physical Chemistry,'' Pearson Benjamin-Cummings, 2006, p.194</ref>