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Boiling-Point Elevation

Also known as colligative boiling

ΔTb=Kb b\Delta T_b = K_b \, b
sig figs

Worked example: Kb = 0.512, b = 1 mol/kg → dT = 0.512 K. Press Try an example to run it live, then adjust anything.

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See also

Freezing-Point Depression with the van 't Hoff Factor: What changes when the solute is a salt: the same van 't Hoff factor i multiplies this equation too.Freezing-Point Depression: Both use molality of solution.Molality (b = n/m): Both use molality of solution.
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Boiling-Point Elevation explained

ΔTbKbb

A non-volatile solute lowers the solvent's vapor pressure, so the solution must be heated a little hotter before that pressure reaches the atmosphere's: the boiling point rises. The rise depends only on how many particles are dissolved, not what they are, scaled by the solvent's ebullioscopic constant Kb. Water's Kb is a modest 0.512 K·kg/mol: a hearty 1.0 mol/kg sugar solution boils at just 100.5 °C, which is why salting pasta water changes its flavor far more than its physics.

Other solvents respond much more strongly (benzene's Kb is 2.53 and camphor's freezing-side cousin is famously huge) and remember that ionic solutes count each ion: 1 mol/kg NaCl acts as nearly 2 mol/kg of particles. Solved backwards, a measured ΔTb divided by Kb gives the molality, the classical route to a dissolved compound's molar mass before mass spectrometers existed.

Boiling-Point Elevation formula

ΔTb=Kb b\Delta T_b = K_b \, b
Where
  • ΔTb\Delta T_b= Boiling-point elevation (C°)
  • KbK_b= Ebullioscopic constant (K·kg/mol)
  • bb= Molality of solution (mol/kg)
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Colligative properties

4 formulasBoiling-point elevation, freezing-point depression, osmotic pressure and Raoult's law — the four effects that count particles, not identity.

Revised 16 October 2026
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formula.expert. (2026, October 16). Boiling-Point Elevation Formula & Calculator. https://formula.expert/solvers/boiling-point-elevation

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