Four calculators, one panel.
Pick a mode below — everything recalculates live as you type, and every result explains itself.
A reactant's concentration falls as the reaction proceeds — the sign is handled for you.
Units for order 1: 1/s
Units for first order: 1/s
A few numbers to an answer.
No manual required — but here's the entire flow in four moves.
Pick a mode
Average rate from a concentration and time interval. Rate law from k and concentrations. Arrhenius for k or Eₐ. Half-life for zero, first or second order reactions.
Enter the known values
Fill in the fields for that mode — concentrations in mol/L, times in seconds, temperatures in K or °C. The example chips fill everything in with one tap so you can see the shape of a working problem.
Read the results
The main answer sits up top in large type. Related values sit below, and the exact formula with your numbers substituted sits at the bottom of the results panel.
Trust the checks
Negative concentrations, a zero time interval, or a coefficient of zero get flagged with a plain-English reason instead of a wrong or broken answer. Copy any result set with one click.
Three equations, one calculator.
Every mode above comes down to one of these three relationships.
Average rate
Change in concentration over time, divided by the coefficient — negative for a reactant, positive for a product, so the reported rate is always positive going forward.
Rate law
The rate constant k multiplied by each reactant's concentration raised to its experimentally measured order. The overall order is m + n.
Arrhenius equation
Links the rate constant k to temperature T and activation energy Eₐ through the pre-exponential factor A and the gas constant R.
Questions people actually ask.
The short answers — with the long ones one tap away.
What is reaction rate?+
Reaction rate is how fast a reactant is consumed or a product is formed, usually expressed as a change in concentration per unit time (mol per litre per second). It tells you how quickly a reaction reaches completion.
How do I calculate the average rate of a reaction?+
Enter the concentration and time at the start and end of the interval, the species' role and coefficient in the Average rate tab. The calculator finds Δ[X] ÷ Δt and divides by the coefficient, flipping the sign for a reactant since its concentration falls as the reaction proceeds.
What is the rate law and how do I use it?+
The rate law is rate = k[A]^m[B]^n, where k is the rate constant and m, n are the experimentally determined orders. Enter k, each concentration and its order in the Rate law tab, and the calculator multiplies them together and reports the overall order.
What does the Arrhenius equation tell me?+
The Arrhenius equation, k = A·e^(−Eₐ ÷ RT), links the rate constant k to temperature T and activation energy Eₐ. The Arrhenius tab solves for k given A, Eₐ and T, or solves for Eₐ if you know k at two different temperatures.
How do I calculate a reaction's half-life?+
Half-life depends on order. Zero order: t½ = [A]₀ ÷ (2k). First order: t½ = ln(2) ÷ k, independent of concentration. Second order: t½ = 1 ÷ (k[A]₀). Pick the order and enter k (and [A]₀ where needed) in the Half-life tab.
Why do rate constant units change with reaction order?+
Rate is always in mol per litre per second, and each concentration term carries its own units, so what's left over for k depends on the overall order: mol/(L·s) for order 0, 1/s for order 1, L/(mol·s) for order 2, and so on.
Is this tool free, and where does my data go?+
It's completely free and runs entirely in your browser — nothing you type is uploaded, logged, or sent to any server. No account, no sign-up, no limits.