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What is the Boiling Point of a Chemical?

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Boiling point is the temperature at which a liquid’s saturated vapor pressure equals its applied pressure, usually the atmospheric pressure. It is a very sensitive measurement to change in pressure, so always report the measured pressure with your results.

Boiling points vary with pressure, temperature and vapour.

The boiling point of a substance is determined by the intermolecular forces between molecules that cause it to go from a liquid state to a gas state (in which case it will boil). There are generally three types of intermolecular forces: London dispersion force, dipole-dipole and hydrogen bonds.

Liquids with high boiling points, such as water, have strong intermolecular forces because their molecules can bond together in very strong ways. The energy needed to break off these connections is much greater than that needed for bonds between weaker molecules.

A higher boiling point also indicates that the chemical is less volatile. This can be important for transporting and storing chemicals.

Addition of solutes can increase a liquid’s boiling point. Solutes like sugar, salt or other non-volatile substances will increase the boiling point of a liquid because they make it more concentrated.

Adding pressure to a liquid can also change its boiling point, because the pressure changes the chemistry of the liquid. For example, when a liquid is heated at the top of Mount Everest it can boil at a lower temperature than sea level because the pressure on the liquid increases.

The van ‘t Hoff factor symbolized with the letter “i” is used to calculate the boiling point elevation of a solution. This constant is also used in equations that give estimates of a chemical’s vapour pressure.