Advanced Topic 458 of 1102 Kinetics & Equilibrium
Chain Reactions
Reactions proceeding through initiation, propagation and termination steps involving reactive intermediates.
Practise Kinetics & Equilibrium All Kinetics & Equilibrium topics
In-depth explanation of Chain Reactions
Chain reactions proceed through a sequence of steps involving reactive intermediates, usually free radicals or atoms. Initiation creates the first radicals, usually by heat or light, propagation steps consume a radical while forming product and generate a new radical, and termination steps remove radicals by combining them. Because propagation regenerates radicals, one initiation event can lead to many product molecules. In branching chains each propagation step can produce more than one radical, which can lead to explosive growth in rate. Chain reactions are central to combustion, polymerization and many atmospheric processes.
Going deeper: Chain Reactions
Key ideas: Count the three stages: initiation makes radicals, propagation keeps them constant in number and builds product, termination removes them. The chain length is the number of product molecules per initiation event, often 10^3 to 10^6. In branching, one radical produces two or more, so the rate grows exponentially and an explosion follows above a critical pressure and temperature.
Common mistakes and connections: Students confuse propagation with termination, or forget that a radical must be formed in each propagation step. Another error is writing a rate law by assuming each step is rate-determining; chain mechanisms are solved with the steady state approximation for radicals. Inhibitors such as antioxidants stop chains. Related to quantum yields above one and to combustion.
Visualization of Chain Reactions
Bond energies explain chain initiation in H2 + Br2: the weak Br-Br bond splits first, giving Br atoms that carry the chain by making strong H-Br bonds. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The reaction H2 + Br2 -> 2HBr proceeds through a radical chain mechanism in which bromine atoms act as chain carriers.
Frequently asked questions about Chain Reactions
What is Chain Reactions?
Reactions proceeding through initiation, propagation and termination steps involving reactive intermediates.
Is Chain Reactions a beginner, intermediate or advanced topic?
Chain Reactions 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 Chain Reactions?
Study these earlier topics in Kinetics & Equilibrium first: Lineweaver-Burk Plot, Enzyme Inhibition, Autocatalysis.
What comes after Chain Reactions?
The next topics in Kinetics & Equilibrium are Oscillating Reactions and Photochemical Reactions.
Can I practise Chain Reactions with quizzes?
Yes. The interactive lesson includes a self-check question on Chain Reactions, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Chain Reactions fits in Kinetics & Equilibrium
Chain Reactions is topic 39 of 91 in Kinetics & Equilibrium.