Kinetics Calculator
Kinetics calculator works out Concentration at t and Rate constant k from What to calculate, Reaction order and Rate constant k. The default figures on this page give concentration at t of 0.367879 mol/L; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
4 steps
- First order: [A]t = [A]0 e^(-k t) = 1 x e^(-0.1 x 10) = 0.36787944117144233 mol/L.
- Fraction remaining: 0.36787944117144233 / 1 = 0.36787944117144233.
- Half-life: 6.931471805599452 s.
- Instantaneous rate at t: k [A]^1 = 0.036787944117144235 mol/(L*s).
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
4 sources
What the kinetics calculator calculates
Solves zero-, first- and second-order integrated rate laws for concentration, time, rate constant and half-life, and applies the Arrhenius equation to relate a rate constant to temperature and activation energy.
How to use this kinetics calculator
Enter What to calculate, Reaction order, Rate constant k and Initial concentration [A]0. Concentration at t updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Concentration at t, Rate constant k and Units of k.
The method follows OpenStax Chemistry 2e, section 12.4 Integrated Rate Laws, OpenStax Chemistry 2e, section 12.5 Collision Theory, IUPAC Compendium of Chemical Terminology (Gold Book), "rate constant" and "Arrhenius equation" and CODATA / SI 2019: molar gas constant R = 8.31446261815324 J/(mol K), exact.
First order, k = 0.1 1/s, [A]0 = 1.0 M, t = 10 s example
With What to calculate: integrated, Reaction order: 1, Rate constant k: 0.1, Initial concentration [A]0: 1, the calculator returns Concentration at t: 0.367879441, Half-life: 6.93147181, Fraction of reactant remaining: 0.367879441. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Concentration at t, Rate constant k and Units of k. The inputs you can vary are What to calculate, Reaction order, Rate constant k, Initial concentration [A]0, Concentration [A]t and Elapsed time.
Understanding Concentration at t, Rate constant k and Units of k
These are idealised single-reactant rate laws. Reaction order, mechanism and thermal behaviour must be established experimentally before the results are used for process design or safety assessment.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How to calculate k in kinetics?
Solves zero-, first- and second-order integrated rate laws for concentration, time, rate constant and half-life, and applies the Arrhenius equation to relate a rate constant to temperature and activation energy. Open “How this is worked out” beside the result to see each step for your own figures.
What information do I need for the kinetics calculator?
You need What to calculate, Reaction order, Rate constant k, Initial concentration [A]0, Concentration [A]t, Elapsed time, Activation energy Ea and Pre-exponential factor A. The page opens with default figures that give concentration at t of 0.367879 mol/L, so you can see the scale before entering your own.
What does this kinetics calculator show?
It shows Concentration at t, Rate constant k, Units of k, Half-life, Reaction rate, Fraction of reactant remaining, Elapsed time and Activation energy, with the working and any warnings for your entries.
Can I check how the kinetics calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.