What is the two-point Arrhenius equation?

By writing the Arrhenius equation for two temperatures and dividing, the pre-exponential factor A cancels: ln(k2/k1) = −(Ea/R) × (1/T2 − 1/T1). Rearranging gives Ea = −R × ln(k2/k1) / (1/T2 − 1/T1). This lets you calculate Ea from just two (k, T) pairs without knowing A.

What units should I use for k1 and k2?

k1 and k2 must have the same units — only their ratio matters in the two-point equation. Use whatever units your experiment produced (s⁻¹, min⁻¹, L·mol⁻¹·s⁻¹, etc.). Both must be positive and non-zero.

Why must T1 and T2 be different?

If T1 = T2 the denominator (1/T2 − 1/T1) is zero, making Ea undefined. You need at least two distinct temperatures to determine the temperature dependence of the rate constant.

Why must temperature be in Kelvin?

The Arrhenius equation uses absolute temperature so that T is never zero or negative. This calculator accepts Celsius input and converts automatically by adding 273.15 K.

What is the pre-exponential factor A, and how is it back-calculated?

A (the frequency factor) is found by rearranging k = A·e^(−Ea/RT) to A = k · e^(Ea/RT). The tool uses k1 and T1 (converted to K) along with the calculated Ea to compute A. Both data points should give the same A; if they differ significantly, the reaction may not follow simple Arrhenius behavior.

What does a large Ea mean for a reaction?

A large activation energy means the reaction is strongly temperature-sensitive: a small temperature increase produces a large jump in k. Reactions with Ea > 80 kJ/mol are considered energetically demanding. Catalysts work by lowering Ea, increasing k without raising temperature.

Activation Energy Calculator

Name: Activation Energy Calculator
Availability: InStock
Author: Nham Vu

Enter two (k, T) data points and get the activation energy Ea using the two-point Arrhenius equation.

Two Data Points

Ea = −R · ln(k₂/k₁) / (1/T₂ − 1/T₁)

Temperature unit

Kelvin (K) Celsius (°C)

Data Point 1

Rate constant k₁

Temperature T₁

Data Point 2

Rate constant k₂

Temperature T₂

Enter two (k, T) pairs and click Calculate Ea.

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Summary

Enter two (k, T) data points and get the activation energy Ea using the two-point Arrhenius equation.

How it works

Enter the rate constant k1 (any positive number) measured at temperature T1.
Enter the rate constant k2 measured at a different temperature T2.
Choose Kelvin or Celsius for the temperature inputs.
Click Calculate — the tool applies ln(k2/k1) = −(Ea/R)(1/T2 − 1/T1) to solve for Ea.
Review the result in both J/mol and kJ/mol, the back-calculated pre-exponential factor A, and the step-by-step substitution.
Click Reset to clear all fields and start a new calculation.

Use cases

Extract activation energy from two rate constant measurements in a kinetics experiment.
Determine Ea without needing to know the pre-exponential factor A.
Verify activation energies calculated by hand before submitting lab reports.
Compare Ea values for catalyzed vs. uncatalyzed reactions.
Prepare for AP Chemistry, MCAT, or physical chemistry exams involving Arrhenius kinetics.
Estimate how much faster a reaction will run at a higher temperature given experimental k data.
Model food spoilage or shelf-life degradation using rate constant ratios.
Screen reaction candidates by comparing Ea values across data points.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu