Ideal solution

An ideal solution is a liquid mixture whose components obey Raoult’s law throughout the full composition range. Its mixing produces no enthalpy or volume change.

Raoult’s law: A relation stating that each component’s partial vapor pressure equals its mole fraction multiplied by its pure-component vapor pressure. It defines the vapor–liquid behavior that every component follows in an ideal solution.
Mole fraction: The amount of a component divided by the total amount of all components in a mixture. Raoult’s law scales each component’s vapor pressure by its liquid-phase mole fraction.
Non-ideal solution: A solution whose components deviate from ideal-solution behavior, such as by violating Raoult’s law. It contrasts directly with mixtures that obey Raoult’s law at every composition.
Vapor–liquid equilibrium: The equilibrium between a liquid mixture and its vapor at specified temperature and pressure. Raoult’s law predicts the vapor composition above an ideal liquid mixture.
Benzene–toluene mixture: A liquid mixture of benzene and toluene, often used to illustrate near-ideal vapor–liquid equilibrium. Similar molecular sizes and intermolecular forces make this pair approximate ideal behavior.
Dalton’s law: A gas-mixture law stating that total pressure equals the sum of the gases’ partial pressures. Combined with Raoult’s law, it gives the ideal solution’s total vapor pressure.
Partial pressure: The pressure contributed by one gas in a mixture, equal to its mole fraction times total pressure for an ideal gas. Each component’s Raoult-law vapor pressure is its partial pressure above the liquid.
Henry’s law: A limiting relation in which a dilute solute’s partial pressure is proportional to its liquid-phase mole fraction. It describes dilute-component behavior where Raoult’s law is not generally the appropriate limit.
Raoult’s law of relative lowering: A relation connecting a nonvolatile solute’s mole fraction to the relative lowering of a solvent’s vapor pressure. It applies the ideal solvent vapor-pressure relation to a solution with a nonvolatile solute.
Hexane–heptane mixture: A liquid mixture of n-hexane and n-heptane with closely related molecular structures and properties. Its similar components make it a common near-ideal mixture example.

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