How to use this calculator
- Select a radioactive or chemical kinetic model.
- Select the unknown value.
- Enter the known values with one consistent time unit.
- Calculate and review the equation used for the selected model.
Formula and variables
zero: t1/2=[A]0/(2k); first: t1/2=ln2/k; second: t1/2=1/(k[A]0)
| Symbol | Meaning | Unit |
|---|---|---|
| t1/2 | half-life | time |
| k | rate constant | order-specific |
| [A]0 | initial concentration | concentration |
Worked example
A first-order rate constant of 0.1 per second gives half-life ln(2)/0.1 = 6.931 seconds.
Interpretation
Each kinetic order has a distinct equation and rate-constant dimension; radioactive decay uses the first-order exponential model explicitly.
Common mistakes
- Do not apply the radioactive/first-order equation to zero- or second-order reactions.
- Keep the rate-constant unit consistent with the chosen kinetic order.
Frequently asked questions
Can the calculator find the remaining radioactive amount?
Yes. Enter the initial amount, elapsed time, and half-life.
Can the calculator find elapsed decay time?
Yes. Enter the initial amount, remaining amount, and half-life.
Do all reaction orders use the same half-life formula?
No. Zero-, first-, and second-order reactions use different equations and rate-constant units.
Can I use scientific notation?
Yes. Enter values such as 6.022e23 or 1.0e-6 in a numeric field.
How should I round the result?
Keep extra digits during the calculation. Round the final result to the precision required by your data.