Chemistry
Reaction Rate Concentration Calculator
Calculate conversion and stoichiometric average rate, then derive apparent zero-, first-, and second-order constants from one concentration interval.
Reactant concentration consumed (mol/L)-
Reactant conversion-
Average disappearance rate (mol/L·s)-
Stoichiometry-normalized reaction rate (mol/L·s)-
Apparent zero-order k (mol/L·s)-
Apparent first-order k (1/s)-
Apparent second-order k (L/mol·s)-
First-order half-life screen (s)-
Decision view
Observed concentration drop with three integrated-law trajectories
Observed concentration drop with three integrated-law trajectoriesThe measured endpoints anchor zero-, first-, and second-order candidate curves so model differences remain visible instead of assuming an order.
Exact scenario comparisonMeasured reactant concentration (mol/L) changes while all other entered assumptions remain constant.
| Measured reactant concentration (mol/L) | Reactant concentration consumed (mol/L) | Reactant conversion | Average disappearance rate (mol/L·s) | Stoichiometry-normalized reaction rate (mol/L·s) | Apparent zero-order k (mol/L·s) | Apparent first-order k (1/s) | Apparent second-order k (L/mol·s) | First-order half-life screen (s) |
|---|
How to use Reaction Rate Concentration Calculator
- Measure initial and later concentrations on the same basis.
- Enter elapsed time and reactant coefficient.
- Compare candidate constants only as a two-point screen.
Calculator guide
Understanding Reaction Rate Concentration Calculator
Two concentration measurements determine an average disappearance rate, but they do not uniquely determine reaction order. This calculator exposes three candidate integrated-law fits.
Detailed calculation process
Detailed concentration-rate calculation
The default reactant falls from 0.8 M to 0.32 M over 180 seconds with coefficient one.
General formula: ΔC=C_0-C_tr_dis=ΔC/Δtr=r_dis/νk_0=(C_0-C_t)/tk_1=ln(C_0/C_t)/tk_2=(1/C_t-1/C_0)/tt_1/2=ln2/k_1 Average rate uses a concentration difference. Candidate constants use different integrated-law transforms of the same endpoints.
What each symbol means
Worked substitution with the default inputs
The default average disappearance rate is 0.002667 M/s; additional time points are required to choose an order.
Worked situations
Practical examples
- The default concentration falls from 0.8 M to 0.32 M in 180 s.
- Average disappearance is 0.002667 M/s; the apparent first-order constant is about 0.005091 s⁻¹.
Better inputs
Useful tips
- Collect at least five well-spaced time points.
- Plot transformed data and residuals.
- Hold temperature and mixing conditions constant.
Before relying on the result
Limitations and common mistakes
- Only two points are fitted.
- Reverse reaction, changing volume, transport limitation, induction, and measurement uncertainty are omitted.
- A declining concentration above the initial value is clamped for disappearance-rate reporting.
Reference
Key terms
- Disappearance rate
- Positive concentration loss divided by elapsed time.
- Integrated rate law
- Concentration-time relationship for an assumed reaction order.
- Half-life
- Time for concentration to halve under the selected model.
Important note
Determine order with replicated multi-time-point experiments, validated analytical measurements, temperature control, and appropriate model diagnostics.
Frequently asked questions
Which k should I use?
Only the constant from an independently supported reaction order.
Why normalize by the coefficient?
Reaction rate convention divides species disappearance by its stoichiometric coefficient.
Is the first-order half-life concentration-independent?
Yes, under a true constant-k first-order model.