Rate Law Calculator

About Rate Law Calculator

The rate law shows how concentration affects reaction rate. The exponents (m, n) are determined experimentally, not from stoichiometry.

How to use this calculator

1. Enter the rate constant \(k\), the concentration of each reactant, and the reaction orders.
2. Use the exponents \(m\) and \(n\) from the rate law, because they tell you how each concentration affects the rate.
3. Check that your units are consistent, then calculate \(rate = k[A]^m[B]^n\).
4. Read the result as the reaction rate for the concentrations you entered.

The formula explained

The formula \(rate = k[A]^m[B]^n\) computes the reaction rate from the rate constant and the reactant concentrations. The exponents \(m\) and \(n\) show the order of the reaction with respect to \(A\) and \(B\).

• rate = reaction rate
• k = rate constant
• [A] = concentration of reactant \(A\)
• m = order with respect to \(A\)
• [B] = concentration of reactant \(B\)
• n = order with respect to \(B\)

Step by step method

1. Write the rate law as \(rate = k[A]^m[B]^n\).
2. Substitute the given values for \(k\), \( [A] \), \(m\), \( [B] \), and \(n\).
3. Evaluate the powers first, then multiply by \(k\).

Worked example

Problem. Find the rate when \(k = 0.50\), \([A] = 2.0\), \([B] = 3.0\), \(m = 1\), and \(n = 2\).

1. Start with \(rate = k[A]^m[B]^n\).
2. Substitute the values: \(rate = 0.50(2.0)^1(3.0)^2\).
3. Compute \( (2.0)^1 = 2.0 \) and \( (3.0)^2 = 9.0 \), then \(rate = 0.50 \\times 2.0 \\times 9.0 = 9.0\).

Tips and common mistakes

• Always apply the exponents to the concentrations before multiplying, because \( [A]^m \) and \( [B]^n \) are part of the rate law.
• Make sure the units of \(k\) match the overall order of the reaction, since the units of rate change with the reaction order.

Frequently asked questions