Reaction rate measures change over time; a rate law describes its dependence under specified conditions.
Key knowledge
Reaction rates describe how quickly reactants are consumed or products formed. A rate law relates a measured rate to composition under specified conditions. For an overall reaction, its reaction orders must be established from kinetic evidence rather than simply copied from the balanced equation's coefficients.
Conditions and scope
State the reaction, temperature, medium and range over which the rate law applies.
Average and instantaneous rates differ; an empirical rate law need not remain valid when conditions or mechanism change.
Sources · 4
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Paul Flowers, Klaus Theopold, Richard Langley and William R. Robinson — OpenStax, Rice University2 sources
Published rate definitions and experimental rate-law determination; no kinetic experiment or parameter fitting was performed.
2026-10-10 · English rate, time-interval and reaction-order distinctions checked against Chemistry 2e sections 12.1 and 12.3; no universal power law asserted.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Agreement within this scope
Consumption/formation rates and experimentally determined reaction orders.
Reaction orders cannot simply be copied from overall stoichiometric coefficients.
Reaction rates describe how quickly reactants are consumed or products formed. A rate law relates a measured rate to composition under specified conditions. For an overall reaction, its reaction orders must be established from kinetic evidence rather than simply copied from the balanced equation's coefficients.
A catalyst provides an alternative reaction pathway that increases the rate and is regenerated in the overall reaction. Catalysed pathways can have lower activation barriers. For the same reversible reaction under fixed thermodynamic conditions, catalysis can hasten the approach to equilibrium without changing its equilibrium constant.
Catalysis changes a reaction pathway and thereby its rate under the specified conditions.
A reaction mechanism is a proposed sequence of elementary steps whose sum yields an overall reaction. For an elementary mass-action step, molecularity determines concentration factors in its rate law. The overall rate law usually requires analysis of the full mechanism.
Proposed elementary steps must be consistent with kinetic evidence.
The Arrhenius model describes many reaction rate constants using a prefactor and an activation-energy parameter. A straight-line dependence of ln k on reciprocal absolute temperature supports the model over the measured range; it does not establish one universal mechanism.
The temperature model describes the stated rate constant over a limited range.
For irreversible loss of one species with constant rate coefficient, integrating −dc/dt=k cⁿ gives c=c₀−kt for n=0, c=c₀e⁻ᵏᵗ for n=1, and 1/c=1/c₀+kt for n=2. Different reaction orders give different time courses and rate-coefficient units.
Integration uses a specified empirical disappearance law.