The key difference between azeotropic and eutectic is that the term azeotropic refers to a mixture of liquids having a constant boiling point whereas the term eutectic refers to chemical mixtures which are liquids that can transform into two solid phases at the same time upon cooling.
The terms azeotropic and eutectic refer to chemical mixtures, but sometimes these terms may have different applications as well; e.g. the term eutectic is sometimes used to name chemical reactions, temperatures (eutectic temperature), or systems (eutectic system).
CONTENTS
1. Overview and Key Difference
2. What is Azeotropic
3. What is Eutectic
4. Side by Side Comparison – Azeotropic vs Eutectic in Tabular Form
5. Summary
What is Azeotropic?
The term azeotropic is used to name a mixture of liquids that has a constant boiling point since the vapour of the liquid mixture has the same composition as the liquid mixture. The boiling point of this mixture can be either higher or lower than any of the individual component of the mixture.
Simple distillation can be used for the separation of components in this mixture since the boiling point of the azeotropic mixture is constant. Hence, we need to use some other techniques: using two distillation columns with different degrees of separation or adding a third compound to the azeotropic mixture in order to change the volatility and boiling point of the components.
What is Eutectic?
The term eutectic mostly refers to chemical reactions that contain a liquid that transforms into two solid phases at the same time upon cooling. A eutectic system is a homogenous mixture of substances that can melt or solidify at a temperature that is lower than the melting point of the constituents in that mixture. Moreover, the term eutectic temperature describes the lowest possible melting temperature for all possible mixing ratios that are involved in the formation of the mixture.
Upon heating a eutectic mixture, the lattice of one component in the mixture will melt first at the eutectic temperature. However, upon cooling the eutectic system, each component in the mixture tends to solidify, forming the lattice of that component at a distinct temperature. Solidification happens until all materials become solids. In general, a eutectic system contains two components; thus, at eutectic temperature, the liquid transforms into two solid phases at the same time and at the same temperature. Thus, we can name this type of reaction as a three-phase reaction. This is a specific type of phase reaction; for example, a liquid solidifies, forming an alpha and beta solid lattices. Here, the liquid phase and solid phase are in equilibrium with each other; a thermal equilibrium.
What is the Difference Between Azeotropic and Eutectic?
The key difference between azeotropic and eutectic is that the term azeotropic refers to liquids having a constant boiling point whereas the term eutectic refers to chemical mixtures which are liquids that can transform into two solid phases at the same time upon cooling. Ethanol in water is an example of an azeotropic mixture while sodium chloride in water is an example of a eutectic system.
The below infographic shows the differences between azeotropic and eutectic in tabular form.
Summary – Azeotropic vs Eutectic
The terms zeotropic and eutectic are used mainly in physical chemistry to refer to specific liquid mixtures. The key difference between azeotropic and eutectic is that the term azeotropic refers to the liquids having a constant boiling point whereas the term eutectic refers to chemical mixtures which are liquids that can transform into two solid phases at the same time upon cooling.
Reference:
1. “Azeotrope.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 19 Feb. 2020, Available here.
2. “Zeotropic Mixture.” Wikipedia, Wikimedia Foundation, 15 Oct. 2019, Available here.
3. “What Is an Azeotrope?” Solvent Recycling and Azeotropes, Available here.
Image Courtesy:
1. “Positive Azeotrope” By WilfriedC at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Eutectic system phase diagram” By Eutektikum_new.svg: *Eutektikum.gif: Dr. Báder Imrederivative work: Michbich (talk)derivative work: Wizard191 (talk) – Eutektikum_new.svg (CC BY-SA 3.0) via Commons Wikimedia