What is boiling point

Boiling point is the temperature at which the vapor pressure of a chemical equals atmospheric pressure. To simply put, it measures the temperature at which a chemical boils. Similar to melting point, a higher boiling point indicates greater inter-molecular forces and therefore less vapour pressure. You can often find it in the section 9 of a safety data sheet SDS.

Cite this Article Format. Helmenstine, Anne Marie, Ph. Definition of Boiling Point in Chemistry. Freezing Point Depression Example Problem. Liquid Elements on the Periodic Table.

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At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. The temperature at which the liquid and vapor phases are in equilibrium with each other at a specified pressure. At the boiling point, the transition from the liquid to the gaseous phase occurs in a pure substance.

Therefore, the boiling point is the temperature at which the vapor pressure of the liquid is equal to the applied pressure on the liquid. The boiling point at a pressure of 1 atmosphere is called the normal boiling point see illustration. For a pure substance at a particular pressure P , the stable phase is the vapor phase at temperatures immediately above the boiling point and is the liquid phase at temperatures immediately below the boiling point see illustration.

The liquid-vapor equilibrium line on the phase diagram of a pure substance gives the boiling point as a function of pressure. Alternatively, this line gives the vapor pressure of the liquid as a function of temperature. The vapor pressure of water is 1 atm The vapor pressure of water is 3. The liquid-vapor equilibrium line on the phase diagram of a pure substance begins at the triple point where solid, liquid, and vapor coexist in equilibrium and ends at the critical point, where the densities of the liquid and vapor phases have become equal.

For pressures below the triple-point pressure or above the critical-point pressure, the boiling point is meaningless. Fossil Fuels. Nuclear Fuels. Acid Rain. Climate Change.