Rate Law Calculator

Determine reaction orders and rate constants from experimental data

Rate Law Calculator

Rate Law: Rate = k[A]m[B]n
Determine reaction orders, rate constant, or reaction rate from experimental data.

Enter data from two experiments (keep one concentration constant):

Notes:

  • • Reaction order must be determined experimentally
  • • Overall order = sum of individual orders (m + n)
  • • Units of k depend on overall reaction order
  • • Keep one concentration constant to determine individual orders

Understanding Rate Laws

The rate law (rate equation) expresses the relationship between the rate of a chemical reaction and the concentrations of reactants. It's determined experimentally and reveals the reaction mechanism.

General Rate Law Form

Rate = k[A]m[B]n

k = Rate Constant

Temperature-dependent constant (increases with temperature)

m, n = Reaction Orders

Must be determined experimentally (not necessarily stoichiometric coefficients)

Overall Order = m + n

Sum of individual orders

Method of Initial Rates

Example: Determine the rate law for: 2NO(g) + O₂(g) → 2NO₂(g)

Exp[NO] (M)[O₂] (M)Rate (M/s)
10.100.102.5 × 10⁻⁵
20.200.101.0 × 10⁻⁴
30.100.205.0 × 10⁻⁵

Step 1: Compare Exp 1 and 2 ([O₂] constant):

Rate₂/Rate₁ = (1.0×10⁻⁴)/(2.5×10⁻⁵) = 4
[NO]₂/[NO]₁ = 0.20/0.10 = 2
4 = 2m → m = 2

Step 2: Compare Exp 1 and 3 ([NO] constant):

Rate₃/Rate₁ = (5.0×10⁻⁵)/(2.5×10⁻⁵) = 2
[O₂]₃/[O₂]₁ = 0.20/0.10 = 2
2 = 2n → n = 1

Rate Law: Rate = k[NO]²[O₂]

Rate Constant Units

Overall OrderUnits of kExample
0M/s or mol/(L·s)Photocatalysis
1s⁻¹ or 1/timeRadioactive decay
2M⁻¹s⁻¹ or L/(mol·s)Bimolecular reactions
3M⁻²s⁻¹ or L²/(mol²·s)Termolecular reactions

Applications

  • 🔬
    Reaction Mechanism: Determining elementary steps and rate-determining step
  • 🏭
    Industrial Optimization: Designing reactors and controlling reaction conditions
  • 💊
    Drug Development: Understanding drug metabolism and stability
  • 🌍
    Environmental Chemistry: Pollutant degradation and atmospheric reactions

⚡Quick Reference

Formula:

Rate = k[A]m[B]n

Determine Order:

Method of initial rates

Key Point:

Orders ≠ stoichiometric coefficients

🔗Related Calculators

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🎯Where It's Used

  • 🧪

    Chemical Kinetics

    Reaction mechanism studies

  • 🏭

    Industrial

    Reactor design