synonyms: (isothermally and isobarically invariant) reaction of double saturation, isothermally invariant reaction
https://doi.org/10.1351/goldbook.15327
Reversible dissolution in a system of three or more components characterized by the composition of a solution that is simultaneously saturated with respect to all (at least two or more) dissolved solutes. The two simultaneous equilibrium processes are, for example, \[\begin{array}{l}\ce{A.p H2O <=> A{(aq, sat)} + p H2O(l)} \\ \ce{B.q H2O <=> B{(aq, sat)} + q H2O(l)}\end{array}\]
Notes:
- The eutonic point is invariant in a ternary system at a given temperature and pressure.
- The chemical potential of solvent decreases along the two solubility curves that intersect at the eutonic point, and thus reaches a minimum value at that point. Thus, colligative properties (that depend on solvent activity) reach a minimum value at the eutonic point. For example, if the solutes are nonvolatile and the solvent is volatile, the vapor pressure reaches a minimum value.
- Eutonic points have been detected in aqueous media only.
- From Greek ευτονος, easy (or lowest) tension (or vapor pressure).
Examples: Systems \(\ce{Na2SO4 + ZnSO4 + H2O}\), \(\ce{Na2SO4 + CdSO4 + H2O}\), \(\ce{Na2SO4 + CuSO4 + H2O}\).
See also: peritonic reaction