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## Ideal solutionIn chemistry, an The concept of an ideal solution is fundamental to chemical thermodynamics and its applications, such as the use of colligative properties. ## Additional recommended knowledge
## Physical originIdeality of solutions is analogous to ideality for gases, with the important difference that intermolecular interactions in liquids are strong and can not simply be neglected as they can for ideal gases. Instead we assume that the mean strength of the interactions are the same between all the molecules of the solution. More formally, for a mix of molecules of A and B, the interactions between unlike neighbors (U If the molecules are almost identical chemically, e.g. 1-butanol and 2-butanol, then the solution will be ideal. Since the interaction energies between A and B are the same, it follows that there is no overall energy (enthalpy) change when the solutions are mixed. The more dissimilar the nature of A and B, the more strongly the solution is expected to deviate from ideality. ## ConsequencesSince the enthalpy of mixing (solution) is zero, the change in Gibbs free energy on mixing is determined solely by the entropy of mixing. Hence the molar Gibbs free energy of mixing is
or for a two component solution - Δ
*G*_{m,mix}=*R**T*(*x*_{A}ln*x*_{A}+*x*_{B}ln*x*_{B})
where m denotes molar i.e. change in Gibbs free energy per mole of solution, and Note that this free energy of mixing is always negative (since each The equation above can be expressed in terms of chemical potentials of the individual components
where Δμ If the chemical potential of pure liquid
where - is the equilibrium vapor pressure of the pure component
- is the mole fraction of the component in solution
It can also be shown that volumes are strictly additive for ideal solutions. ## Non-idealityDeviations from ideality can be described by the use of Margules functions or activity coefficients. A single Margules parameter may be sufficient to describe the properties of the solution if the deviations from ideality are modest; such solutions are termed In contrast to ideal solutions, where volumes are strictly additive and mixing is always complete, the volume of a non-ideal solution is not, in general, the simple sum of the volumes of the component pure liquids and solubility is not guaranteed over the whole composition range. ## See also## References
Categories: Solutions | Thermodynamics |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ideal_solution". A list of authors is available in Wikipedia. |