vapor pressure

This term is a technical specification used primarily in chemistry, physics, and thermodynamics. It describes the tendency of molecules to escape from a liquid or solid phase into a gaseous phase. A substance with high vapor pressure is described as volatile, meaning it evaporates quickly at room temperature.

In a practical sense, vapor pressure is the key variable in determining boiling points; when the vapor pressure of a liquid reaches the surrounding atmospheric pressure, the liquid begins to boil. Because it is a specific physical property of a substance, it is treated as an uncountable concept in scientific discourse.