Raoult's law Calculator
Partial vapour pressure of a component in an ideal solution.
Formula first
Overview
Raoult's law states that the partial vapor pressure of a component in an ideal solution is equal to the product of its mole fraction in the liquid phase and the vapor pressure of the pure component. This principle assumes that the intermolecular forces between unlike molecules are equal to those between like molecules in the pure substances.
Symbols
Variables
x_i = Mole Fraction, P_i^* = Pure Vapour Pressure, P_i = Partial Pressure
Apply it well
When To Use
When to use: Apply this equation when analyzing ideal mixtures where components have similar chemical structures and molecular sizes. It is most accurate for dilute solutions or mixtures of non-polar liquids like benzene and toluene at low to moderate pressures.
Why it matters: This law provides the theoretical basis for colligative properties such as vapor pressure lowering and boiling point elevation. It is a critical tool for chemical engineers designing distillation processes to separate chemical mixtures based on volatility.
Avoid these traps
Common Mistakes
- Applying to non-ideal solutions without correction.
- Confusing partial and total pressure.
One free problem
Practice Problem
A chemical solution contains a component with a mole fraction of 0.60. If the vapor pressure of the pure component at this temperature is 120.0 mmHg, calculate the partial vapor pressure exerted by this component in the mixture.
Solve for:
Hint: Multiply the given mole fraction by the vapor pressure of the pure substance.
The full worked solution stays in the interactive walkthrough.
References
Sources
- Atkins' Physical Chemistry
- Wikipedia: Raoult's law
- Bird, Stewart, Lightfoot, Transport Phenomena
- IUPAC Gold Book: 'mole fraction'
- IUPAC Gold Book: 'partial pressure'
- Bird, Stewart, Lightfoot - Transport Phenomena
- Atkins' Physical Chemistry (11th ed.)
- IUPAC Gold Book (entry for 'Raoult's law', 'ideal solution')