Rate law Calculator

Formula first

Overview

The rate law mathematically relates the speed of a chemical reaction to the molar concentrations of its reactants. It utilizes a proportionality constant called the rate constant, k, and reactant orders, m and n, which indicate how sensitive the rate is to changes in each substance's concentration.

Symbols

Variables

k = Rate Constant, [A] = Concentration of A, [B] = Concentration of B, m = Order wrt A, n = Order wrt B

Apply it well

When To Use

When to use: Apply this equation when you need to calculate the instantaneous speed of a reaction or determine the reaction order from experimental kinetic data. It is valid under conditions where temperature is held constant, as the rate constant k is temperature-dependent.

Why it matters: This formula is fundamental for designing safe chemical reactors and predicting the shelf-life of pharmaceuticals. By identifying the reaction order, chemists can deduce the molecular mechanism and sequence of steps occurring at the atomic level.

Avoid these traps

Common Mistakes

• Using stoichiometric coefficients as orders.
• Forgetting units of k depend on order.

One free problem

Practice Problem

A reaction has the rate law: rate = k[A][B]^2. The rate constant k = 0.015 $d{m}^6$ mol^-2 s^-1. If [A] = 0.3 mol/$d{m}^3$ and [B] = 0.2 mol/$d{m}^3$, calculate the reaction rate.

Solve for: rate

Hint: rate = k[A]^m[B]^n. Square [B] first, then multiply all terms.

The full worked solution stays in the interactive walkthrough.

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Related Formulas

References

Sources

1. Atkins' Physical Chemistry
2. Wikipedia: Rate law
3. Atkins' Physical Chemistry, 11th Edition
4. IUPAC Gold Book (Reaction rate, Rate constant, Order of reaction)
5. Bird, Stewart, Lightfoot - Transport Phenomena, 2nd Edition
6. Atkins' Physical Chemistry, 11th Edition, Peter Atkins, Julio de Paula, James Keeler
7. IUPAC Gold Book (Compendium of Chemical Terminology)
8. Wikipedia: Rate equation