What is the rate law?

The rate law (or rate equation) expresses reaction rate as: rate = k[A]^m[B]^n... where k is the rate constant, [A] and [B] are molar concentrations of reactants, and m and n are the reaction orders with respect to each reactant.

What are the units of the rate constant k?

The units of k depend on the overall reaction order. For a zero-order reaction: mol/(L·s); first-order: 1/s; second-order: L/(mol·s); third-order: L²/(mol²·s). This tool accepts any numeric value for k — just keep units consistent.

What does reaction order mean?

The reaction order with respect to a reactant indicates how the rate changes when that reactant's concentration changes. A first-order reactant doubles the rate when its concentration doubles; a second-order reactant quadruples the rate, and so on.

Can the reaction order be a fraction or zero?

Yes. Reaction orders are determined experimentally, not from stoichiometry. They can be zero (rate independent of that reactant), fractions (e.g. 0.5), negative (rate decreases as concentration rises), or positive integers.

What is the overall reaction order?

The overall reaction order is the sum of all individual orders (m + n + ...). This tool calculates and displays it automatically.

How accurate is this calculator?

The calculation uses standard floating-point arithmetic (IEEE 754 double precision), which is accurate to about 15 significant digits — more than enough for chemistry problems.

Rate Law Calculator

Enter the rate constant and up to four reactants with their concentrations and reaction orders to calculate the overall reaction rate.

Rate Law Inputs

Rate Constant (k)

Reactants

Fill in the inputs and click Calculate Rate

Rate Law Expression

Reaction Rate

Overall Order

sum of all orders

Calculation Breakdown

Reactant	[Conc] (M)	Order	[C]^n
Product of terms (∏[C]ⁿ)

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Summary

The rate law calculator computes the instantaneous reaction rate using the expression rate = k[A]^m[B]^n... for up to four reactants. Enter the rate constant k, each reactant's molar concentration, and its experimentally determined reaction order. The tool evaluates the expression, displays the symbolic rate law, the overall reaction order, and the numeric result — making it easy to solve chemical kinetics problems without manual exponentiation.

How it works

Enter the rate constant (k).
Add one or more reactants by entering a name, concentration (mol/L), and reaction order.
Click "Calculate Rate" to compute the reaction rate.
The tool displays the full rate law expression and the numeric result.
Adjust any value and recalculate to explore how rate depends on each reactant.

Use cases

Determine reaction rate from experimental concentration and k data.
Verify hand-calculated rate law expressions in chemistry coursework.
Explore how doubling a reactant concentration affects rate for different orders.
Set up and solve chemical kinetics problems in physical chemistry.
Check units consistency for rate constants of various reaction orders.
Demonstrate the difference between zero-order, first-order, and second-order kinetics.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu