The vapor pressure of a liquid is defined as the pressure exerted by the molecules that escapes from the liquid to form a separate vapor phase above the liquid surface.
The pressure exerted by the vapor phase is called the

  • vapor or saturation pressure

Vapor or saturation pressure depends on temperature.
If a fluid consist of more than one component (a solution), components with

  • higher vapor pressure are called light components
  • lower vapor pressure are called heavy components

[h=Temperature and Vapor or Saturation Pressure for some common Fluids]3[/h] At atmospheric pressure saturation temperature of

  • water : 100oC
  • ethyl alcohol : 78.5oC