Activation Energy Calculator
Find an Arrhenius activation energy from a rate constant and frequency factor, or from measurements at two temperatures.
01 Set up your calculation
- Choose a single-temperature calculation or two measured rate constants.
- Use the same rate units and reaction order for every rate constant and frequency factor.
- Enter absolute temperatures, or select a temperature unit for conversion, and read the molar activation energy.
02 The relationship
For the assumptions behind these results, read the explanation below. You can also explore Arrhenius Equation and Gibbs Free Energy.
Follow the numbers
At 300 K, A = 1,000,000 and k = 0.01 in matching units give Eₐ = 8.314462618 × 300 × ln(100,000,000) = 45.9474 kJ/mol.
03 Interpreting an apparent energy barrier
Activation energy describes how strongly a measured rate constant changes with temperature within an Arrhenius model. It is an energy per mole, not the heat released by a reaction. A reaction can release energy overall and still have a substantial kinetic barrier.
The single-temperature result depends on the supplied frequency factor. Use a factor measured or fitted for the same mechanism and units; an arbitrary factor cannot reveal a unique physical activation energy.
04 Using two measurements carefully
The two-point form removes the unknown frequency factor by assuming it is constant over the temperature interval. Small errors are amplified when the two temperatures are close together. Several temperature measurements and a fitted Arrhenius plot generally give more reliable evidence than a single pair.
A negative apparent activation energy is retained rather than silently changed to zero. It can occur in complex mechanisms or signal inconsistent data. The result does not prove that an elementary collision has a negative barrier.
Questions from the notebook
Can I enter Celsius?
Yes, through the unit control. The equation is evaluated in kelvin, and zero or negative kelvin is rejected.
Do k and A need units of s⁻¹?
Only for a first-order rate constant. Other reaction orders use different units, but k and A must match.
Does a catalyst change this result?
A catalyst may provide a different mechanism and a different temperature dependence. Compare measurements from the same catalytic conditions.
References & reading
- OpenStax, Rice University — Collision Theory ↗
Explains the Arrhenius equation, its logarithmic form, activation energy, and temperature dependence.
- NIST — Guide to SI conversion factors ↗
Supports physical unit conversions. Input values are converted to the formula’s base units before calculation.
Our explanations are written for ChemistryCalc. Read how we build and check our tools. These calculations are educational estimates where the underlying model requires assumptions.