The passage of molecules from the surface of a liquid into the gaseous, or vapor state is called vaporization or evaporation. Evaporation is frequently used when liquid phase converted into gas phase at a temperature below the boiling point of liquid. Solution The passage of molecules from the surface of a liquid into the gaseous, or vapor state is called vaporization or evaporation. Evaporation is frequently used when liquid phase converted into gas phase at a temperature below the boiling point of liquid..