Ebullioscopic constant

Template:Short description Template:Use American English Template:More citations needed In thermodynamics, the ebullioscopic constant Template:Math relates molality Template:Mvar to boiling point elevation. It is the ratio of the latter to the former:

$\mathrm{\Delta }{T}_{\text{b}}=i{K}_{\text{b}}b$

• Template:Mvar is the van 't Hoff factor, the number of particles the solute splits into or forms when dissolved.
• Template:Mvar is the molality of the solution.

A formula to compute the ebullioscopic constant is:

$K_{\text{b}}=\frac{RM{T}_{\text{b}}^2}{1000\mathrm{\Delta }{H}_{\text{vap}}}$

• Template:Mvar is the ideal gas constant.
• Template:Mvar is the molar mass of the solvent.
• Template:Math is boiling point of the pure solvent in kelvin.
• Template:Math is the molar enthalpy of vaporization of the solvent.

Through the procedure called ebullioscopy, a known constant can be used to calculate an unknown molar mass. The term ebullioscopy means "boiling measurement" in Latin. 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 Template:Math, depends on the number of particles dissolved into the solvent and not the nature of those particles.

Values for some solvents

Solvent	Template:Math (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

• Ebullioscope
• List of boiling and freezing information of solvents
• Boiling-point elevation
• Colligative properties

External links

• Ebullioscopic constant calculator AD

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