Reaction Rate Calculator
Average reaction rate in M per second.
What it does
Reaction rates clock concentration change per second: start minus end over time for disappearance. This page averages one window in molarity per second.
The default runs 1 M to 0.4 M over 60 s. Change is 0.6 M and the average rate is 0.01 M/s. A faster window at 2 to 0.5 M over 50 s averages 0.03 M/s the same way.
Averages hide slowdowns. Most reactions brake as reactants drain, so early windows read hotter than late ones and instant rates need curve slopes. Catalysts, temp, and surface reset the whole shape.
Signs set meaning. Disappearance runs positive here while formation flips negative; keep one convention per report so tables compare.
How to use
- Enter start molarity.
- Enter end molarity.
- Enter seconds elapsed.
- Read rate first, then change.
- Use slopes for instant rates.
Formula
- start
- Starting molarity.
- end
- Ending molarity.
- time
- Elapsed seconds.
Average disappearance rate over the window; instant rates need tangent slopes at a point. Formation rates take the negative sign. Units stay molarity per second throughout.
Worked example
Example: 0.6 M in a minute
1 M to 0.4 M over 60 s.
- Change: 1 - 0.4 = 0.6 M.
- Divide: 0.6 / 60 = 0.01 M/s.
- Check: 0.01 x 60 = 0.6 M back.
- Tool shows 0.01 M/s with 0.6 M change.
- Average only; instant rates need slopes.
Reference table
| Time | Rate | Note |
|---|---|---|
| 30 s | 0.02 M/s | Fast window |
| 60 s | 0.01 M/s | Default |
| 120 s | 0.005 M/s | Slow window |
| 300 s | 0.002 M/s | Long tail |
| 600 s | 0.001 M/s | Very slow |
Limits
- Average only. No instant slopes.
- One window per pass.
- No order, k, or mechanism.
- Disappearance convention.
Common mistakes
- Reading average as instant.
- Dropping units to bare numbers.
- Mixing minutes with seconds.
- Forgetting formation signs.
- Comparing windows of mixed length.
Try it yourself
Quick checks. Answers sit tucked under each question.
2 M to 0.5 M over 50 s?
0.03 M/s (1.5 / 50).
1 M to 0.5 M over 100 s?
0.005 M/s (0.5 / 100).
Questions
Average rate?
Change over time. Here 0.01 M/s.
Change?
Start minus end. Here 0.6 M.
Formation rates?
Yes for formation with signs flipped. This page uses disappearance.
Rate law?
No. Order, k, and mechanisms sit outside averages.
Same always?
No. Catalysts and temp shift it.
Rising concentration?
End above start fails here. Swap for formation.