Reaction Rate Calculator

Calculate reaction rate from rate constant and concentrations using rate = k[A]^m[B]^n. Solve for any variable in the rate law for first, second, or zero order reactions.

⏱️ Kinetics📐 rate = k[A]^m[B]^n🧪 Chemistry
Rate constant k
[A] concentration (mol/L)
[B] concentration (mol/L)
Order m for A
Order n for B
Units of k
Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
Reaction Rate CalculatorSee formularate = k[A]^m[B]^nmol/L·s

Step-by-Step Examples

Example 1
First Order

A to B. Rate = k[A]. k=0.0500 s^-1, [A]=0.200 M.

  • rate = 0.0500 x 0.200
  • rate = 0.0100 mol/Ls
✓ rate = 0.0100 mol/L-s
Example 2
Second Order

2NO + O2 to 2NO2. rate=k[NO]^2[O2]. k=7.1x10^9 M^-2s^-1, [NO]=0.010 M, [O2]=0.020 M.

  • rate = 7.1x10^9 x (0.010)^2 x 0.020
  • rate = 7.1x10^9 x 10^-4 x 0.020 = 1.42x10^4 mol/Ls
✓ rate = 1.42x10^4 mol/L-s
Example 3
Rate Doubling

First order: [A] doubles from 0.10 to 0.20 M. How does rate change?

  • rate proportional to [A]^1
  • rate doubles: new rate = 2 x old rate
✓ First order: doubling [A] doubles rate

Real-World Applications

🏭
Chemical Manufacturing
Rate laws guide reactor design and optimal operating conditions.
💊
Pharmacokinetics
Drug elimination follows first-order kinetics: rate of elimination proportional to concentration.
🌍
Atmospheric Chemistry
Rate laws for ozone depletion reactions guide environmental policy.
🧪
Catalysis Research
Comparing rates with and without catalyst reveals catalytic mechanism.

Common Mistakes to Avoid

⚠️
Rate law comes from experiment only

Cannot determine rate law from balanced equation. Must be determined experimentally by measuring rate vs concentration.

⚠️
Units of k depend on overall order

Zero order: mol/Ls. First order: s^-1. Second order: L/mols. Third order: L^2/mol^2s.

⚠️
Rate is instantaneous, not average

Rate = d[product]/dt at a specific moment. Concentration changes over time; rate changes too.

Frequently Asked Questions

What is a rate law? ▾
Mathematical expression: rate = k[A]^m[B]^n. k is rate constant. m and n are reaction orders (found experimentally). Overall order = m+n.
How do I find reaction order experimentally? ▾
Method of initial rates: measure rate at different concentrations. If doubling [A] doubles rate, m=1. If rate quadruples, m=2.
What is a pseudo-first-order reaction? ▾
When one reactant is in large excess, its concentration stays essentially constant, so effective rate = k_eff[A] even if true order is higher.
What are the units of k for different orders? ▾
Zero: mol/(L-s). First: 1/s. Second: L/(mol-s). The units make the rate have units of mol/(L-s) in all cases.
Does rate constant depend on concentration? ▾
No. k depends only on temperature (Arrhenius equation) and catalyst presence. It is constant at fixed T.

Related Chemistry Calculators

⏱️ Rate Constant k🌡️ Arrhenius Equation⏱️ Half-Life Chemistry⏱️ Integrated Rate Law🌡️ Activation Energy

Formula Explorer connections

Interpretation: This formula connects concentration, time, temperature or transport to the speed of a chemical process. Assumption: The reaction order and mechanism must match the model. Temperature, catalyst, mixing and mass-transfer limitations can alter the observed rate.

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