Rate Constant Calculator
Determine the rate constant for zero, first or second-order kinetics.
About Rate Constant Calculator
Each reaction order has its own integrated rate law and its own units for k. Only first-order reactions have a concentration-independent half-life, which is why radioactive decay is described so simply. Fitting data to the wrong order gives a k that drifts with concentration, which is itself the diagnostic that the order is wrong.
Formula
Rate Constant
Zero: k = ([A]₀−[A])/t; first: k = ln([A]₀/[A])/t; second: k = (1/[A] − 1/[A]₀)/t
- order
- Power to which concentration is raised in the rate law
- half-life
- Constant only for first-order reactions
Worked example
With the default values below, Rate Constant Calculator returns Rate Constant of 0.00462098. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Initial concentrationminimum 0 mol/L
- 1 mol/L
- Concentration after time tminimum 0 mol/L
- 0.25 mol/L
- Time elapsedminimum 0.001 s
- 300 s
- Reaction orderone of Zero order, First order, Second order
- First order
Results
- Rate Constant
- 0.00462098
- Half-Life
- 150.0000 s
- Units of the Rate Constant
- per second
- Time for 63% Conversion
- 216.4043 s
- Conversion Achieved
- 75.000%
Step by step
- 1Values used
- 2Rate Constant
- 3Rate Constant= 0.00462098
- 4Half-Life= 150.0000 s
- 5Units of the Rate Constant= per second
- 6Time for 63% Conversion= 216.4043 s
- 7Conversion Achieved= 75.000
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 8 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Rate Constant calculated?
Zero: k = ([A]₀−[A])/t; first: k = ln([A]₀/[A])/t; second: k = (1/[A] − 1/[A]₀)/t Each reaction order has its own integrated rate law and its own units for k. Only first-order reactions have a concentration-independent half-life, which is why radioactive decay is described so simply.
Why does Rate Constant matter?
Fitting data to the wrong order gives a k that drifts with concentration, which is itself the diagnostic that the order is wrong.
What values do I need to enter?
This calculator takes 4 inputs: Initial concentration, Concentration after time t, Time elapsed, Reaction order. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.