Raoult's Law Calculator
Vapour pressure lowering, in proportion to mole fraction.
Work out Raoult's Law. Vapour pressure lowering, in proportion to mole fraction. Says where the approximation breaks.
23.8 mmHg for water at 25 °C.
Vapour pressure of solution
21.42
Lowered by 2.38 · 10.00%
P = χ·P°. A non-volatile solute lowers vapour pressure in exact proportion to the solvent's mole fraction, because fewer solvent molecules sit at the surface to escape. This is the same effect that raises the boiling point: the solution must be heated further before its vapour pressure reaches atmospheric.
How the Raoult's Law Calculator works
P = χ·P°. A non-volatile solute lowers vapour pressure in exact proportion to the solvent's mole fraction, because fewer solvent molecules sit at the surface to escape. This is the same effect that raises the boiling point.
Also known as: vapour pressure lowering calculator · vapor pressure of a solution · relative lowering of vapour pressure · raoult's law formula
Frequently asked questions
What is Raoult's law?
The vapour pressure of a solution equals the pure solvent's vapour pressure times the solvent's mole fraction. A mole fraction of 0.9 gives 90% of the pure pressure.
How does this relate to boiling point elevation?
Directly. Lower vapour pressure means the solution must be heated further before its vapour pressure reaches atmospheric — which is what boiling is.
When does Raoult's law fail?
For concentrated solutions and for mixtures where the two components interact differently with each other than with themselves. It is an ideal-solution law, exact only in the dilute limit.
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