Average Reaction Rate Calculator
Find the average rate of a chemical reaction from the change in concentration over a time interval, adjusted for stoichiometry.
How it works
rate of species = |[final] − [initial]| ÷ Δt · rate of reaction = rate of species ÷ stoichiometric coefficient
The average reaction rate is the change in concentration of a species divided by the time over which it occurs, taken as a positive quantity. Because reactants and products change at rates tied to their coefficients, dividing by the species’ stoichiometric coefficient gives the single "rate of reaction" that is the same no matter which species you track.
Worked example
A reactant falls from 0.80 M to 0.20 M over 40 s with a coefficient of 1: rate = |0.20 − 0.80| ÷ 40 = 0.60 ÷ 40 = 0.015 mol/(L·s).
Sources: Reaction rate — Wikipedia
Frequently asked questions
Why divide by the stoichiometric coefficient?
In a reaction like 2A → B, A disappears twice as fast as B forms. Dividing each species’ rate by its coefficient yields one consistent rate of reaction that everyone agrees on.
What is the difference between average and instantaneous rate?
Average rate is the change over a finite interval. Instantaneous rate is the slope of the concentration-time curve at a single moment — the limit as the interval shrinks to zero.
Why is the rate always positive?
Rate is expressed as a positive number by convention. For a reactant whose concentration decreases, a minus sign is applied so the reported rate stays positive.
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This calculator is for educational purposes. Double-check important results before acting on them.