Reaction Rate Law Calculator
A rate law tells you how fast a reaction proceeds given the concentrations of its reactants. It takes the form rate equals the rate constant times each reactant concentration raised to its experimentally determined order. Those orders are measured from rate data and are not always the stoichiometric coefficients. This calculator evaluates the rate for a reaction in up to two reactants from the rate constant, the two concentrations, and their orders, and also reports the overall reaction order. Enter your measured orders and concentrations in consistent units.
Rate law formula
rate = k * [A]^m * [B]^n
overall order = m + n
(set an order to 0 to drop a reactant from the rate law)
The rate constant and concentrations must be zero or greater, and concentrations raised to nonzero orders must be positive. The rate carries the units implied by k and the concentrations.
Rate law context
- Reaction orders are determined experimentally, not from the balanced equation coefficients.
- The overall order is the sum of the individual reactant orders.
- The units of k depend on the overall order so that rate stays as concentration per time.
- A zero-order reactant does not affect the rate; its order term equals one.
- The rate constant rises with temperature according to the Arrhenius equation.
Rate law: frequently asked questions
What is a rate law?
A rate law expresses the reaction rate as the rate constant times the concentrations of the reactants each raised to an order: rate = k [A]^m [B]^n. The orders m and n are found experimentally and are not necessarily the stoichiometric coefficients.
What is the rate constant k?
The rate constant k is a proportionality factor specific to a reaction at a given temperature. Its units depend on the overall reaction order so that the rate always has units of concentration per time. A larger k means a faster reaction.
What is the overall reaction order?
The overall order is the sum of the individual reactant orders in the rate law. For rate = k [A]^1 [B]^2 the overall order is 3. The overall order sets the units of the rate constant and how the rate responds to dilution.
Are reaction orders the same as coefficients?
Not in general. Reaction orders are determined experimentally and reflect the mechanism, while stoichiometric coefficients come from the balanced equation. They coincide only for an elementary reaction step, so enter orders measured from rate data.
What units does the rate have?
Reaction rate is expressed as a change in concentration per unit time, commonly mol per liter per second. This calculator returns the rate in the concentration and time units implied by your rate constant and concentration inputs.
Official sources
- IUPAC Gold Book: rate law, order of reaction and rate constant terminology.
- NIST Chemistry WebBook: kinetics and thermochemical reference data.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.