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In thermodynamics, the ebullioscopic constant Kb relates molality b to boiling point elevation.[1] It is the ratio of the latter to the former:

A formula to compute the ebullioscopic constant is:[2]

Through the procedure called ebullioscopy, a known constant can be used to calculate an unknown molar mass. The term ebullioscopy comes from the Latin language and means "boiling measurement". This is related to cryoscopy, which determines the same value from the cryoscopic constant (of freezing point depression).

This property of elevation of boiling point is a colligative property. It means that the property, in this case ΔT, depends on the number of particles dissolved into the solvent and not the nature of those particles.

Values for some solvents

Solvent[3] Kb (in K⋅kg/mol)
Acetic acid 3.08
Benzene 2.53
Camphor 5.95
Carbon disulfide 2.34
Carbon tetrachloride 5.03
Chloroform 3.63
Cyclohexane 2.79
Diethyl ether 2.02
Ethanol 1.07
Water 0.512

See also


  1. ^ "Ebullioscopic Constant". CHEMISTRY GLOSSARY.
  2. ^ Martin, Chaplin. "Colligative Properties". London South Bank University. London South Bank University.
  3. ^ P. W. Atkins, Physical Chemistry, 4th Ed., p. C17 (Table 7.2)