What Is a Volatile Substance in Chemistry?

In chemistry, the word "volatile" refers to a substance that vaporizes readily. Volatility is a measure of how readily a substance vaporizes or transitions from a liquid phase to a gas phase. The term can also be applied to the phase change from a solid state to vapor, which is called sublimation. A volatile substance has a high vapor pressure at a given temperature compared with a nonvolatile compound.

Examples of Volatile Substances

• Mercury is a volatile element. Liquid mercury had a high vapor pressure, readily releasing particles into the air.
• Dry ice is a volatile inorganic compound that sublimates at room temperature from the solid phase into carbon dioxide vapor.
• Osmium tetroxide (OsO₄) is another volatile inorganic compound that, like dry ice, transitions from the solid phase to the vapor phase without becoming a liquid.
• Many organic compounds are volatile. For example, alcohol is volatile. Because volatile substances readily vaporize, they mix with air and can be smelled (if they have an odor). Xylene and benzene are two volatile organic compounds with distinctive scents.

Relationship Between Volatility, Temperature, and Pressure

The higher the vapor pressure of a compound, the more volatile it is. Higher vapor pressure and volatility translate into a lower boiling point. Increasing temperature increases vapor pressure, which is the pressure at which the gas phase is in equilibrium with the liquid or solid phase.