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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 Modern Theory of Solutions: Memoirs by Pfeffer, Van't Hoff, Arrhenius, and Raoult. New York: Harper and Brothers. (Contains reprints of three papers by Raoult) General Law of the Freezing of Solutions (Comptes Rendus 95, 1030 - 1033, 1882) General Law of the Vapor Pressure of Solvents (Comptes Rendus 104, 1430 - 1433, 1887)
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.
The simplest definition is that an ideal solution is a solution for which each component obeys Raoult's law = for all compositions. Here p i {\displaystyle p_{i}} is the vapor pressure of component i {\displaystyle i} above the solution, x i {\displaystyle x_{i}} is its mole fraction and p i ∗ {\displaystyle p_{i}^{*}} is the vapor pressure ...
For an ideal solution, the equilibrium vapor pressure is given by Raoult's law as = + +, where is the vapor pressure of the pure component (i= A, B, ...) and is the mole fraction of the component in the solution.
K is the distribution coefficient or K factor, defined as the ratio of mole fraction in the vapor phase () to the mole fraction in the liquid phase () at equilibrium. When Raoult's law and Dalton's law hold for the mixture, the K factor is defined as the ratio of the vapor pressure to the total pressure of the system: [ 1 ]
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.
This means that, at least at low concentrations, the vapor pressure of the solvent will be greater than that predicted by Raoult's law. For instance, for solutions of magnesium chloride , the vapor pressure is slightly greater than that predicted by Raoult's law up to a concentration of 0.7 mol/kg, after which the vapor pressure is lower than ...