Calculate a reaction rate constant and half-life from concentration change over time for zero, first and second order reactions.
Result
How to use this tool
Use the same unit for both.
Use the time unit you want in k.
If unsure, test which order gives a constant k.
Half-life formulas differ by order.
Formula & worked example
A first-order reaction falling from 100 to 50 in 10 time units has k = 0.0693 per time unit and a half-life of 10.
Limitations — read this before you rely on it
Single-time-point calculation; it cannot establish the reaction order on its own.
Frequently asked questions
They depend on order: concentration/time (zero), 1/time (first), 1/(concentration·time) (second).
No — check that k stays constant across several time points.
Only for first order. For zero and second order it depends on the starting concentration.
Any consistent unit; k’s unit follows from it.
That finds k from temperature and activation energy; this finds k from measured concentrations.