Reaction Half Life Calculator Form
Concentration Decay Plot
Example Data Table
| Reaction Order | Initial Concentration | Rate Constant | Half-Life | Time Unit |
|---|---|---|---|---|
| Zero order | 1.2000 mol/L | 0.1500 mol·L⁻¹·min⁻¹ | 4.0000 min | min |
| First order | 1.0000 mol/L | 0.2000 min⁻¹ | 3.4657 min | min |
| Second order | 0.5000 mol/L | 0.8000 L·mol⁻¹·min⁻¹ | 2.5000 min | min |
Formula Used
Zero-order half-life: t1/2 = [A]₀ / 2k
First-order half-life: t1/2 = ln(2) / k
Second-order half-life: t1/2 = 1 / k[A]₀
Zero-order concentration: [A]t = [A]₀ − kt
First-order concentration: [A]t = [A]₀e−kt
Second-order concentration: 1 / [A]t = 1 / [A]₀ + kt
The calculator automatically switches formula sets based on selected reaction order and calculation mode. This helps compare kinetics without manually rearranging equations.
How to Use This Calculator
- Select the calculation mode that matches your chemistry problem.
- Choose zero, first, or second reaction order.
- Enter the initial concentration and other required values.
- Pick suitable concentration and time units for your data.
- Set decimal precision for cleaner reporting.
- Press the calculate button to display the result above the form.
- Review the summary table and concentration decay chart.
- Export the calculated output as CSV or PDF when needed.
Frequently Asked Questions
1. What does reaction half-life mean?
Reaction half-life is the time required for the concentration of a reactant to drop to half of its initial value under a defined kinetic model.
2. Why does half-life depend on reaction order?
Different reaction orders change how concentration influences reaction speed. Because the rate law changes, the half-life equation also changes for zero, first, and second order systems.
3. Is first-order half-life independent of initial concentration?
Yes. For first-order reactions, half-life depends only on the rate constant. Changing the starting concentration does not change the half-life value.
4. When should I use the remaining concentration mode?
Use it when you already know the rate constant and elapsed time, and need to estimate how much reactant remains after decay.
5. Can this calculator estimate time to reach a threshold?
Yes. The target concentration mode solves for elapsed time needed to reach a chosen concentration, based on the selected reaction order and rate constant.
6. What units should I use for rate constant?
Use units consistent with reaction order and time. First-order often uses time⁻¹, while zero and second order require concentration-dependent unit forms.
7. Why might zero-order concentration reach zero quickly?
Zero-order decay decreases concentration linearly with time. If the time interval is long enough, the model can predict complete depletion earlier than exponential models.
8. Does the graph update after calculation?
Yes. After submission, the plot refreshes using the active kinetics settings, showing concentration decay over time and a vertical reference at half-life.