O

Order of Reaction

r = k[A]^m[B]^n
Quick Reference
Formula / Notationr = k[A]^m[B]^n
Also Known AsReaction 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.

Key Facts

Term Order of Reaction
Formula r = k[A]^m[B]^n
Synonyms Reaction 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.

More "O" Terms

View all "O" terms →
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z