The key difference between eutectoid reaction and peritectic reaction is that eutectoid reaction is the conversion of one solid phase into two other solid phases, whereas peritectic reaction is the conversion of a liquid phase and a solid phase into a different solid phase.
A eutectoid reaction is a chemical reaction in which a solid transforms into two other solid phases at the same time upon cooling. A peritectic reaction is a chemical reaction in which a solid phase and liquid phase collectively form a second solid phase at a particular temperature and composition. These terms are important in describing phase diagrams.
CONTENTS
1. Overview and Key Difference
2. What is a Eutectoid Reaction
3. What is a Peritectic Reaction
4. Eutectoid Reaction vs Peritectic Reaction in Tabular Form
5. Summary – Eutectoid Reaction vs Peritectic Reaction
What is a Eutectoid Reaction?
A eutectoid reaction is a chemical reaction in which a solid transforms into two other solid phases at the same time upon cooling. This is a three-phase reaction because one phase of matter turns into two other phases of matter. It is an isothermal reaction that forms two mixed solid phases. The number of solids in the solid mixture depends on the number of components in the system.
A eutectoid reaction occurs at the eutectoid point. This reaction is similar to the eutectic reaction; the difference is in the phases that are changing. The eutectoid reaction of iron is an example of this reaction. The eutectoid structure of iron has a special name: pearlite. Pearlite is a mixture of two phases: ferrite and cementite. This structure occurs in many common grades of steel, which is an alloy of iron and carbon.
What is a Peritectic Reaction?
A peritectic reaction is a chemical reaction in which a solid phase and liquid phase collectively form a second solid phase at a particular temperature and composition. For example, the combination of a liquid with an alpha solid form may give the beta form of solid. Therefore, it is a three-phase reaction. Upon cooling, the liquid phase reacts with a solid phase to form a new, single solid phase.
Peritectic reactions are isothermic and reversible reactions. This means the reaction takes place at the same temperature level, and the reaction can be moved backward to get the reactant/can be reversed.
Moreover, there is a peritectic point in a graph showing a peritectic reaction. This is the point on the phase diagram at which a reaction occurs in between a previously precipitated phase and the liquid for the production of a new solid phase. At this point, the temperature remains constant until the reaction completes. Further, a peritectic point is an invariant point.
What is the Difference Between Eutectoid Reaction and Peritectic Reaction?
Eutectoid reactions and peritectic reactions are important in describing phase diagrams. The key difference between eutectoid reaction and peritectic reaction is that eutectoid reactions refer to the conversion of one solid phase into two other solid phases, whereas a peritectic reaction refers to the conversion of a liquid phase and a solid phase into a different solid phase.
The below infographic presents the differences between eutectoid reaction and peritectic reaction in tabular form for side by side comparison.
Summary – Eutectoid Reaction vs Peritectic Reaction
A eutectoid reaction is a chemical reaction in which a solid transforms into two other solid phases at the same time upon cooling. A peritectic reaction is a chemical reaction in which a solid phase and liquid phase collectively form a second solid phase at a particular temperature and composition. The key difference between eutectoid reaction and peritectic reaction is that a eutectoid reaction is the conversion of one solid phase into two other solid phases, whereas a peritectic reaction is the conversion of a liquid phase and a solid phase into a different solid phase.
Reference:
1. “Peritectic Reaction.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “Peritectic” By Sk5040 – Own work (CC BY-SA 3.0) via Commons Wikimedia