In
thermodynamics
Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...
, the ebullioscopic constant relates
molality
In chemistry, molality is a measure of the amount of solute in a solution relative to a given mass of solvent. This contrasts with the definition of '' molarity'' which is based on a given volume of solution.
A commonly used unit for molality ...
to
boiling point elevation. It is the ratio of the latter to the former:
:
* is the
van 't Hoff factor, the number of particles the solute splits into or forms when dissolved.
* is the
molality
In chemistry, molality is a measure of the amount of solute in a solution relative to a given mass of solvent. This contrasts with the definition of '' molarity'' which is based on a given volume of solution.
A commonly used unit for molality ...
of the solution.
A formula to compute the ebullioscopic constant is:
:
* is the
ideal gas constant.
* is the
molar mass
In chemistry, the molar mass () (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical substance ( element or compound) is defined as the ratio between the mass () and the amount of substance ...
of the solvent.
* is
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envi ...
of the pure
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvÅ'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
in
kelvin
The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...
.
* 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
In chemistry, the molar mass () (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical substance ( element or compound) is defined as the ratio between the mass () and the amount of substance ...
. The term ''ebullioscopy'' means "boiling measurement" in
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
. 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 , depends on the number of particles dissolved into the solvent and not the nature of those particles.
Values for some solvents
See also
*
Ebullioscope
*
List of boiling and freezing information of solvents
*
Boiling-point elevation
*
Colligative properties
References
External links
Ebullioscopic constant calculatorAD
Phase transitions
{{Thermodynamics-stub