What Is a Rate Law Reaction Order Calculator?
In chemical kinetics, the "order" of a reaction with respect to a reactant describes how strongly the reaction rate responds to that reactant's concentration. This calculator applies the method of initial rates: comparing two trials where only one reactant's concentration changes reveals that reactant's order.
This is the standard two-trial technique used throughout general and physical chemistry kinetics courses, before combining individual orders into a full rate law.
How to Read Your Results
Reaction Order (n)
This is the calculated exponent for this reactant in the rate law, rate = k[A]^n. It's usually close to a whole number.
Rate Ratio & Concentration Ratio
These show how many times faster the reaction became (rate ratio) versus how many times more concentrated the reactant became (concentration ratio) between the two trials — the raw numbers behind the order calculation.
Closest Common Order
Real lab data rarely gives a perfectly clean integer. This rounds your result to the nearest common order (zero, first, second or third) when it's close enough, and flags it as non-integer otherwise.
Real-World Example
Trial 1: rate = 0.020 M/s at [A] = 0.10 M. Trial 2: rate = 0.080 M/s at [A] = 0.20 M (all other reactants held constant).
| Quantity | Value |
|---|---|
| Rate ratio | 0.080 ÷ 0.020 = 4.0× |
| Concentration ratio | 0.20 ÷ 0.10 = 2.0× |
| Reaction order n | ln(4.0) ÷ ln(2.0) = 2.0 |
Doubling the concentration quadrupled the rate, so this reactant is second order — its exponent in the rate law is 2.
Tips for Determining Reaction Order
- Change only one concentration at a time. If more than one reactant changes between trials, this two-trial method won't isolate the order correctly.
- Use initial rates, measured before the reaction has progressed far enough for products to interfere.
- Repeat with a third trial to confirm the order and check for experimental consistency.
- Sum the individual orders for all reactants to get the overall reaction order.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team