What is the Arrhenius equation?

The Arrhenius equation k = A·e^(−Ea/RT) relates the rate constant k of a chemical reaction to temperature T, the activation energy Ea, and the pre-exponential factor A. R is the universal gas constant (8.314472 J/mol·K).

What units does Ea use?

Activation energy Ea is most often given in joules per mole (J/mol) or kilojoules per mole (kJ/mol). This calculator accepts both — switch the unit selector before entering your value, and the tool converts internally.

What is the pre-exponential factor A?

A (also called the frequency factor or attempt frequency) represents the maximum possible rate constant — the rate if every collision had enough energy to react. Its units match the units of k, which depend on the reaction order (e.g., s⁻¹ for first-order reactions).

How do I find Ea from two temperatures?

Use the two-point Arrhenius form: ln(k2/k1) = −(Ea/R)·(1/T2 − 1/T1). Rearranging gives Ea = −R·ln(k2/k1) / (1/T2 − 1/T1). This calculator handles single-point solving; for the two-point form, solve for Ea by entering k = k2/k1, A = 1, and (1/T2 − 1/T1) manually, or use the two-point mode by selecting "Solve for Ea" with two k/T pairs.

Why must temperature be in Kelvin?

The Arrhenius equation requires absolute temperature in Kelvin so that T is never zero or negative, which would make the exponent undefined. This calculator accepts Celsius input and converts it automatically by adding 273.15.

What does a higher activation energy mean?

A higher Ea means fewer molecules have enough thermal energy to overcome the barrier, resulting in a smaller rate constant k at a given temperature. Such reactions are also more sensitive to temperature changes — the rate increases more steeply per degree of warming.

Arrhenius Equation Calculator

Name: Arrhenius Equation Calculator
Availability: InStock
Author: Nham Vu

Enter any three of the four Arrhenius variables (k, A, Ea, T) and instantly solve for the fourth using k = A·e^(−Ea/RT).

Inputs

k = A · e^−Ea/RT

Solve for

Rate Constant (k)

s⁻¹

Units depend on reaction order; must be > 0.

Pre-exponential Factor (A)

same as k

Must be > 0. Scientific notation (1.5e13) is accepted.

Activation Energy (Ea)

Temperature (T)

Select what to solve for, fill in the other values, then click Calculate.

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Summary

Enter any three of the four Arrhenius variables (k, A, Ea, T) and instantly solve for the fourth using k = A·e^(−Ea/RT).

How it works

Choose which variable you want to solve for: k, A, Ea, or T.
Enter values for the remaining three variables in the input fields.
Select the units for Ea (J/mol or kJ/mol) and for T (K or °C) as needed.
Click Calculate; the tool applies the Arrhenius equation and rearranges it algebraically for the chosen unknown.
Review the result, the step-by-step equation breakdown, and the ln(k) vs. 1/T slope note.
Click Reset to clear all fields and start a new calculation.

Use cases

Determine how much faster a reaction runs when temperature increases.
Extract activation energy Ea from two rate constants measured at different temperatures.
Solve general chemistry and physical chemistry homework problems involving reaction kinetics.
Predict the rate constant at a new temperature given a known Ea and A.
Verify hand-calculated Arrhenius results before submitting lab reports.
Explore the sensitivity of k to small changes in activation energy or temperature.
Prepare for AP Chemistry, MCAT, or university kinetics exams.
Model industrial reaction rates to estimate process conditions.

Frequently Asked Questions

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Last updated: 2026-05-28 · Reviewed by Nham Vu