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Why don't chemical reactions reach stability? How nature creates change in chemistry!
In our daily lives, chemical reactions always seem to be developing towards a certain stable state. However, when it comes to specific chemical reactions, it all presents a completely different picture. These reactions, called chemical oscillatory reactions, are complex mixtures of chemical systems in which the concentration of one or more components changes periodically. These reactions demonstrate the characteristics of nonequilibrium thermodynamics and provide an important perspective for our understanding of changes in nature.
These reactions show that chemical reactions do not have to be dominated by equilibrium thermodynamic behavior.
Representatives of chemical oscillation reactions include the famous Belousov–Zhabotinsky reaction (BZ reaction), Briggs–Rauscher reaction and Bray–Liebhafsky reaction. Not only are these reactions interesting, they are also of great scientific interest because they show how the dynamics and changes of chemical systems resist reaching a steady state.
The history of oscillatory reactions
In the history of science, early evidence of these oscillatory reactions was met with great skepticism. As early as 1828, G.T. Fechner published a report describing oscillation phenomena in a chemical system, including an electrochemical cell that produced an oscillating current. Then in 1899, W. Ostwald observed that the dissolution rate of chromium in acid periodically increased and decreased. However, at that time it was thought to only exist in heterogeneous systems, while homogeneous oscillatory systems were thought not to exist. As the 20th century progressed, the limitations of this research became a consensus among the scientific community at the time.
“A system that reacts with oscillations will not oscillate around an ultimate equilibrium position because such oscillations would violate the second law of thermodynamics.”
It was not until the mid-1970s that the systematic study of oscillatory chemical reactions and nonlinear chemical kinetics gradually took shape. In these systems, reactions that release energy can follow at least two different pathways, with regular switching between pathways. This behavior has led scientists to study the internal dynamics of chemical reactions.
Mathematical models and mechanisms
Models by mathematicians and chemists suggest that the concentrations of certain reaction intermediates oscillate. These models include the Lotka-Volterra model, Brusselator and Oregonator (the latter is specifically used to simulate the Belousov-Zhabotinsky reaction). In these reactions, the concentration of intermediates can directly influence the reaction path choice, leading to novel dynamic behaviors.
“These models not only help us understand chemical oscillation phenomena, but also provide a theoretical basis for our in-depth understanding of non-equilibrium systems.”
Types of chemical oscillation reactions
Belousov–Zhabotinsky (BZ) reaction
The Belousov–Zhabotinsky reaction is a well-known oscillatory chemical system. This reaction, which contains both bromine and acid components, is an important example of studying self-organizing patterns. This phenomenon was first described by Boris Belousov in the 1950s, in which cerium ions in two different oxidation states undergo periodic reduction and oxidation, causing the solution color to change between yellow and colorless.
Briggs–Rauscher reaction
The Briggs–Rauscher reaction is a remarkable chemical oscillation reaction known for its wonderful color changes. A freshly prepared colorless solution gradually changes to amber, then suddenly to dark blue, then rapidly fades again, and the process repeats itself. This color change makes it an important demonstration for observing and learning chemistry.
Bray–Liebhafsky reaction
The Bray–Liebhafsky reaction, first described by W.C. Bray in 1921, is a chemical reaction involving the oxidation and reduction of iodine. This reaction exhibits the periodicity of chemical changes and provides the basis for our understanding of chemical kinetics.
From these examples, we can't help but ask, how many mysteries and wisdom of nature are hidden behind these seemingly ever-changing chemical reactions?
