Advanced Topic 457 of 1102 Kinetics & Equilibrium
Autocatalysis
A reaction in which a product acts as a catalyst, giving sigmoidal concentration profiles.
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In-depth explanation of Autocatalysis
In an autocatalytic reaction one of the products acts as a catalyst for its own formation, so the reaction starts slowly and then accelerates as the product builds up. The rate law therefore contains the product concentration as well as the reactant concentration, and the rate rises before falling again as reactants are consumed. The concentration of the product against time has a characteristic sigmoidal, or S-shaped, profile. Autocatalysis is important in crystal nucleation, in some polymerization reactions and in biochemical pathways. It also explains induction periods, during which a reaction appears to do nothing before it suddenly speeds up.
Going deeper: Autocatalysis
Key ideas: A simple model is A + P -> 2P with rate = k[A][P], giving a logistic S-shaped curve with maximum rate when [A] equals [P]. The induction period is shorter when a little product is added at the start, a quick test for autocatalysis. A plot of rate against time shows a rise then a fall, unlike normal decay.
Common mistakes and connections: Students mistake the slow start for an inactive reaction or think it contradicts the rate law, which is largest at the start. For autocatalysis the initial rate is small because [P] is small. Another error is to mix up autocatalysis with a catalyst added from outside. It is the root of oscillating reactions, and of explosions caused by heat build-up, known as thermal autocatalysis.
Visualization of Autocatalysis
The product speeds up its own formation, giving an S-shaped curve: a slow induction period, rapid acceleration, then levelling off as reactant runs out. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The oxidation of oxalate by permanganate is catalysed by Mn2+ ions, which are themselves a product of the reaction.
Frequently asked questions about Autocatalysis
What is Autocatalysis?
A reaction in which a product acts as a catalyst, giving sigmoidal concentration profiles.
Is Autocatalysis a beginner, intermediate or advanced topic?
Autocatalysis is a advanced topic in Kinetics & Equilibrium. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Autocatalysis?
Study these earlier topics in Kinetics & Equilibrium first: Michaelis-Menten Kinetics, Lineweaver-Burk Plot, Enzyme Inhibition.
What comes after Autocatalysis?
The next topics in Kinetics & Equilibrium are Chain Reactions and Oscillating Reactions.
Can I practise Autocatalysis with quizzes?
Yes. The interactive lesson includes a self-check question on Autocatalysis, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Autocatalysis fits in Kinetics & Equilibrium
Autocatalysis is topic 38 of 91 in Kinetics & Equilibrium.