Define the Vapor Pressure

The partial pressure exerted at the surface of a liquid at the liquid/vapor interface. The liquid molecules are released into the vapor phase when the liquid boils. Boiling occurs when the vapor pressure of the liquid exceeds the vapor pressure above the liquid - usually atmospheric pressure. Vapor pressure is a function of temperature only. Increasing a liquid's temperature increases its vapor pressure.

Greek symbol:  none    

Units: lb/ft²    

lb/in² = psi = (lb/ft²)(ft²/144 in²)