Calculate a rate constant or reaction rate
A rate constant calculator evaluates the general rate law rate = kΠ[Ai]^ni. Enter one row for each reactant with a unique name, positive concentration in mol/L, and its reaction order. Choose whether rate or k is unknown. The page multiplies the concentration powers in logarithmic form, reports total order, and derives the rate-constant unit associated with that order.
Use reaction orders from experimental data or an explicitly justified elementary step. They are not automatically the stoichiometric coefficients in a balanced overall equation. The calculator accepts zero, fractional, and negative orders within a bounded teaching range because empirical rate laws can use them, but the chemical meaning must come from the stated kinetic model.
Understand the general rate law and k units
For rate = k[A]^m[B]^n, total order is m + n. Solving for k divides the measured rate by both concentration powers; solving for rate multiplies k by them. With rate in mol L−1 s−1 and concentrations in mol/L, the rate-constant unit is (mol/L)^(1−total order) s−1. A first-order law therefore gives s−1.
Zero order gives concentration per time, second order gives L mol−1 s−1, and noninteger total orders retain a corresponding fractional power. Unit analysis is a useful check, but it cannot determine the correct order. The same numerical k written with the wrong concentration or time unit represents a different quantity, so keep the unit and temperature beside every reported rate constant.
Follow a multi-reactant rate law example
Suppose rate = k[A][B]^2, with [A] = 0.20 mol/L, [B] = 0.10 mol/L, and measured rate = 0.004 mol/L·s. The concentration product is 0.20 × 0.10^2 = 0.002. Dividing rate by that product gives k = 2 with third-order units (mol/L)^−2·s−1.
A reverse check multiplies k = 2 by the same concentration product and recovers 0.004 mol/L·s. Doubling A doubles rate in this model, while doubling B multiplies rate by four. These proportional checks are often easier to reason about than the final decimal and can reveal a transposed order or an exponent accidentally applied to the wrong concentration.
Interpret k without confusing kinetics and equilibrium
The rate constant depends on temperature and can also change with catalyst, solvent, ionic strength, pressure, or reaction pathway. Changing concentration changes the rate predicted by one fixed law but should not change k under unchanged conditions. An Arrhenius calculation addresses temperature dependence; an equilibrium constant addresses the equilibrium composition. Neither should be substituted for the kinetic rate constant.
A rate law is often valid only over the conditions used to establish it. Mechanism changes, saturation, diffusion control, induction periods, reversibility, or product inhibition can invalidate a single power-law expression. Use residual analysis and repeated measurements for experimental kinetics, and do not extrapolate a fitted k far outside its verified temperature or concentration range.
Kinetic-model limits, safety, and privacy
A calculated rate does not establish that a reaction is safe to run. Thermal accumulation, gas generation, mixing, heat transfer, pressure relief, and scale can dominate real process risk. Use measured kinetics, uncertainty, calorimetry, and qualified process-safety review for consequential work. This page supplies transparent arithmetic for a stated rate law, not a mechanism or hazard assessment.
The values are calculated in the current browser tab. NexaCurrent does not upload the quantities, formulas, chemical names, element choices, or other information entered here, and no account is needed. Copying is a deliberate action after the answer and working are visible. Refreshing or leaving the page clears the current calculation, so keep a copied result if it is needed for later study.