Title: eutonic reaction
Long Title: IUPAC Gold Book - eutonic reaction
DOI: 10.1351/goldbook.15327
Status: current

Definition
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
1) The eutonic point is invariant in a ternary system at a given temperature and pressure.
2) 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.
3) Eutonic points have been detected in aqueous media only.
4) From Greek ευτονος, easy (or lowest) tension (or vapor pressure).

Example
Systems \(\ce{Na2SO4 + ZnSO4 + H2O}\), \(\ce{Na2SO4 + CdSO4 + H2O}\), \(\ce{Na2SO4 + CuSO4 + H2O}\).

Related Terms
- components: https://goldbook.iupac.org/terms/view/16268
- peritonic reaction: https://goldbook.iupac.org/terms/view/15344
- ternary system: https://goldbook.iupac.org/terms/view/15366

Source
- PAC, 2008, 80, 233. 'Glossary of terms related to solubility (IUPAC Recommendations 2008)' on page 246 (https://doi.org/10.1351/pac200880020233)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/15327/html
- json: https://goldbook.iupac.org/terms/view/15327/json
- xml: https://goldbook.iupac.org/terms/view/15327/xml

Citation: Citation: 'eutonic reaction' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.15327
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Accessed: 2026-05-09T20:43:01+00:00