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Raoult's law (/ ˈ r ɑː uː l z / law) is a relation of physical chemistry, with implications in thermodynamics.Proposed by French chemist François-Marie Raoult in 1887, [1] [2] it states that the partial pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component (liquid or solid) multiplied by its mole fraction in the mixture.
The vapor pressure affects the solute shown by Raoult's Law while the free energy change and chemical potential are shown by Gibbs free energy. Most solutes remain in the liquid phase and do not enter the gas phase, except at very high temperatures. In terms of vapor pressure, a liquid boils when its vapor pressure equals the surrounding pressure.
For liquid solutions, the osmotic coefficient is often used to calculate the salt activity coefficient from the solvent activity, or vice versa. For example, freezing point depression measurements, or measurements of deviations from ideality for other colligative properties, allows calculation of the salt activity coefficient through the osmotic coefficient.
Köhler theory combines the Kelvin effect, which describes the change in vapor pressure due to a curved surface, with Raoult's Law, which relates the vapor pressure to the solute concentration. [1] [2] [3] It was initially published in 1936 by Hilding Köhler, Professor of Meteorology in the Uppsala University.
An ideal solution or ideal mixture is a solution that exhibits thermodynamic properties analogous to those of a mixture of ideal gases. [1] The enthalpy of mixing is zero [2] as is the volume change on mixing by definition; the closer to zero the enthalpy of mixing is, the more "ideal" the behavior of the solution becomes.
These are analogous to Boyle's law and Charles's law for gases. Similarly, the combined ideal gas law , P V = n R T {\displaystyle PV=nRT} , has as an analogue for ideal solutions Π V = n R T i {\displaystyle \Pi V=nRTi} , where Π {\displaystyle \Pi } is osmotic pressure; V is the volume; n is the number of moles of solute; R is the molar gas ...
Mole fraction vs. temperature diagram for a two-component system, showing the bubble point and dew point curves. In thermodynamics, the bubble point is the temperature (at a given pressure) where the first bubble of vapor is formed when heating a liquid consisting of two or more components.
Raoult's law is applicable only to non-electrolytes (uncharged species); it is most appropriate for non-polar molecules with only weak intermolecular attractions (such as London forces). Systems that have vapor pressures higher than indicated by the above formula are said to have positive deviations.