AllChemicals — The Online Chemical Glossary | https://allchemicals.info/chemical/637-order-of-reaction
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Quick Reference
Formula / Notation
r = k[A]^m[B]^n
Also Known As
Reaction order, kinetic order, rate law exponent, overall reaction order
What is Order of Reaction?
The power to which the concentration of a reactant is raised in the experimentally determined rate law. Overall order is the sum of individual orders. Zero order: rate independent of concentration. First order: rate proportional to concentration. Determined from experimental data.
Formula & Notation
r = k[A]^m[B]^n
Other Names / Synonyms: Reaction order, kinetic order, rate law exponent, overall reaction order
Properties & Characteristics
The order of a reaction is the sum of the exponents in the rate law: r = k[A]^m[B]^n (overall order = m + n). Individual orders (m, n) are determined experimentally (not from stoichiometry, unless the reaction is an elementary step). Reactions can be zero-order (rate independent of concentration), first-order (rate ∝ [A]: half-life t₁/₂ = 0.693/k), second-order (rate ∝ [A]² or [A][B]), or fractional-order (for complex mechanisms). The rate constant k has units that depend on the overall order.
Uses & Applications
Reaction order is used in: predicting how concentration changes affect rate (important for reactor design), calculating half-lives of radioactive decay (always first-order: t₁/₂ = 0.693/k), pharmacokinetics (first-order drug elimination gives predictable half-life), and in kinetic modelling of industrial reactions.
Safety Information
Zero-order reactions (rate constant, regardless of concentration) can be deceptive — doubling concentration does not double the reaction time but rate stays constant; however, if concentration suddenly increases (e.g., liquid spill into a zero-order surface reaction), the reaction continues at full rate with more material available. Understanding reaction order is crucial for process safety analysis.
Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.
SynonymsReaction order, kinetic order, rate law exponent, overall reaction order
Frequently Asked Questions
The power to which the concentration of a reactant is raised in the experimentally determined rate law. Overall order is the sum of individual orders. Zero order: rate independent of concentration. First order: rate proportional to concentration. Determined from experimental data.
Reaction order is used in: predicting how concentration changes affect rate (important for reactor design), calculating half-lives of radioactive decay (always first-order: t₁/₂ = 0.693/k), pharmacokinetics (first-order drug elimination gives predictable half-life), and in kinetic modelling of indus…
Zero-order reactions (rate constant, regardless of concentration) can be deceptive — doubling concentration does not double the reaction time but rate stays constant; however, if concentration suddenly increases (e.g., liquid spill into a zero-order surface reaction), the reaction continues at full …
The formula or notation for Order of Reaction is: r = k[A]^m[B]^n
Editorial standards: Chemical data is sourced from peer-reviewed literature,
CAS Registry, NIST WebBook, and PubChem. Safety information reflects guidance from OSHA, ECHA,
and IAEA. For educational purposes only — always consult official SDS documentation and qualified
professionals before handling chemicals.
