Reaction Rate Calculator

This calculator evaluates the rate law Rate = k × [A]^m × [B]^n, where the rate constant k and the reaction orders m and n with respect to each reactant are experimentally determined values — they cannot be read off a balanced equation the way stoichiometric coefficients can, so the orders you enter should come from actual kinetics data for your reaction, not a guess. Overall reaction order is simply m + n, and it governs how sensitive the rate is to concentration changes: a first-order reactant doubling its concentration doubles the rate, a second-order reactant doubling its concentration quadruples it, and a zero-order reactant (order 0) can change concentration with no effect on rate at all. Half-life is only computed for the two textbook-simple cases this engine recognizes: a reaction that is first order overall (order 1 in A, order 0 in B, or effectively first order some other way), where half-life is a constant ln(2)/k independent of concentration, and a reaction that is second order in a single reactant (order 2 in A, order 0 in B), where half-life is 1/(k×[A]) and does depend on the starting concentration.

Outside those two shapes — for instance a mixed-order reaction with both A and B contributing — the half-life field reports zero rather than a fabricated number, since there's no simple closed-form expression for it. A frequent mixup is treating the rate constant's units as fixed: k's units actually shift with overall order (s⁻¹ for first order, M⁻¹s⁻¹ for second order, and so on), so a k value pulled from a reference table only applies if you match its implied order to what you enter here.