Reaction Order Calculator (Method of Initial Rates)
Order of a reaction with respect to one reactant from two experiments with different starting concentrations, plus the rate constant and the predicted rate at another concentration.
Results
What this tool does
Change one concentration, keep everything else fixed, and see how the initial rate responds: if doubling the concentration doubles the rate the order is 1, if it quadruples it the order is 2, and if nothing happens the order is 0. The order is found from the experiment itself and can be a fraction; it is not read off the balanced equation, which is the usual trap. Repeat the pair of experiments for each reactant, and use initial rates so that products have not yet built up to slow or speed the reaction.
Formula
n = ln(rate₂ ÷ rate₁) ÷ ln(c₂ ÷ c₁) · k = rate₁ ÷ c₁ⁿ · rate = k cⁿ
Variables
| Symbol | Meaning | Unit |
|---|---|---|
c1 | Concentration in experiment 1 | mol/L |
r1 | Initial rate in experiment 1 | mol/(L·s) |
c2 | Concentration in experiment 2 | mol/L |
r2 | Initial rate in experiment 2 | mol/(L·s) |
c3 | Concentration to predict the rate at | mol/L |
N | Order of the reaction in this reactant | — |
K | Rate constant k (units depend on the order) | — |
R3 | Predicted rate at that concentration | mol/(L·s) |
DF | Rate multiplier if the concentration doubles | × |
Worked example
- Concentration in experiment 10.1 mol/L
- Initial rate in experiment 10.002 mol/(L·s)
- Concentration in experiment 20.2 mol/L
- Initial rate in experiment 20.008 mol/(L·s)
- Concentration to predict the rate at0.5 mol/L
- Order of the reaction in this reactant2.000
- Rate constant k (units depend on the order)0.20000
- Predicted rate at that concentration0.050000 mol/(L·s)
- Rate multiplier if the concentration doubles4.00 ×
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.