R

Rate Law

Rate = k[A]^m[B]^n
Quick Reference
Formula / NotationRate = k[A]^m[B]^n
Also Known AsRate expression, Kinetic rate equation, Rate equation

What is Rate Law?

A mathematical expression relating the rate of a chemical reaction to the concentrations of reactants raised to experimentally determined powers: Rate = k[A]ᵐ[B]ⁿ. The exponents (m, n) are the reaction orders, determined experimentally, not from the balanced equation (unless elementary).

Formula & Notation

Rate = k[A]^m[B]^n

Other Names / Synonyms: Rate expression, Kinetic rate equation, Rate equation

Properties & Characteristics

Rate constant k depends on temperature via Arrhenius equation: k = A × exp(−Ea/RT). Reaction orders (m, n) are determined experimentally, NOT from stoichiometry unless the step is elementary. Zero order: rate = k (constant, t½ = [A]₀/2k). First order: rate = k[A] (t½ = 0.693/k). Second order: rate = k[A]² (t½ = 1/k[A]₀). Units of k vary: for first order = s⁻¹; second order = M⁻¹s⁻¹.

Uses & Applications

Predicting reaction rates under varying concentration and temperature conditions. Chemical reactor design and optimization. Pharmacokinetics — drug metabolism follows first-order kinetics. Food preservation and shelf-life modeling. Atmospheric chemistry: ozone depletion rate calculations. Radioactive decay modeling. Environmental contaminant degradation.

Safety Information

Understanding rate laws is essential for identifying fast and potentially violent reactions. First-order kinetics governs radioactive half-lives — critical for radiation exposure calculations. Activation energy data helps predict explosion risks at elevated temperatures.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Rate Law
Formula Rate = k[A]^m[B]^n
Synonyms Rate expression, Kinetic rate equation, Rate equation

Frequently Asked Questions

A mathematical expression relating the rate of a chemical reaction to the concentrations of reactants raised to experimentally determined powers: Rate = k[A]ᵐ[B]ⁿ. The exponents (m, n) are the reaction orders, determined experimentally, not from the balanced equation (unless elementary).

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