Reaction Rate Calculator
The rate of a chemical reaction is described by the rate law: rate = k * [A]^n, where k is the rate constant (units depend on order), [A] is the molar concentration of reactant A, and n is the order of the reaction with respect to A. This calculator computes the instantaneous rate for a single-reactant rate law. For reactions with two reactants, the rate would be k * [A]^m * [B]^n; this tool handles one reactant at a time. Enter the rate constant, concentration, and reaction order to find the rate.
Rate law formula
rate = k * [A]^n
Where k is the rate constant, [A] is the concentration of reactant A in mol/L, and n is the reaction order with respect to A. The rate is in mol/L per unit time. Units of k must be consistent so the rate comes out in mol L^-1 s^-1.
Reaction orders and rate behavior
- Zero-order (n=0): rate = k. Rate is constant, independent of concentration. k units: mol L^-1 s^-1.
- First-order (n=1): rate = k[A]. Rate proportional to concentration. k units: s^-1. Half-life = 0.693/k.
- Second-order (n=2): rate = k[A]^2. Rate proportional to concentration squared. k units: L mol^-1 s^-1.
- Overall order = sum of all individual orders in the rate law.
Frequently asked questions
What is the rate law for a chemical reaction?
The rate law expresses the reaction rate as a function of reactant concentrations: rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are concentrations, and m and n are the orders with respect to each reactant.
What is the reaction order?
The reaction order (n) indicates how the rate depends on concentration. For a first-order reaction (n=1), doubling [A] doubles the rate. For second-order (n=2), doubling [A] quadruples the rate. Zero-order (n=0) means rate is independent of [A].
What are the units of the rate constant k?
Units of k depend on the overall reaction order. For first-order: s^-1. For second-order: L mol^-1 s^-1. For zero-order: mol L^-1 s^-1. The units must make the rate come out in mol L^-1 s^-1.
How is rate constant k determined?
k is determined experimentally by measuring reaction rates at known concentrations and temperatures, then using the integrated rate law or initial rate method. k values are tabulated in NIST databases for many reactions.
How does temperature affect the rate constant k?
k increases with temperature according to the Arrhenius equation: k = A * exp(-Ea/RT), where Ea is the activation energy, R is the gas constant, and T is temperature in Kelvin. A 10-degree rise often roughly doubles k.
Official sources
- IUPAC Gold Book: Rate of reaction definition.
- NIST Chemical Kinetics Database: NIST kinetics data.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.