Activation Energy Calculator
Explore temperature, reaction rates and the Arrhenius relationship.
Kinetic measurements
Activation energy & temperature response
Two-point Arrhenius estimate · 300 K → 330 K
Arrhenius plot
Two-point fitk₀ = 1 s⁻¹ · slope = −Eₐ/R. Preview follows the fitted model.
Reaction energy profile
IllustrativeSingle-step teaching diagram. ΔH is supplied separately; an Arrhenius Eₐ is not necessarily a microscopic barrier height.
Temperature sensitivity
The same fitted model at selected temperatures.
| Temperature | Rate constant | vs. 300 K |
|---|---|---|
| 280 K | 1.638e-04 s⁻¹ | 0.16× |
| 300 K | 1.000e-03 s⁻¹ | 1.00× |
| 315 K | 3.340e-03 s⁻¹ | 3.34× |
| 330 K | 1.000e-02 s⁻¹ | 10.00× |
| 350 K | 3.728e-02 s⁻¹ | 37.28× |
This example has positive apparent Eₐ, so the modeled rate rises with temperature. Negative apparent activation energies need different interpretation.
What changes when temperature rises?
Collision theoryA conceptual view of molecular motion — not a particle simulation or a predicted reaction yield.
Particles have a lower average kinetic energy. Individual energies still vary throughout the sample.
The energy distribution shifts. For a conventional activated reaction, more collisions can have sufficient energy.
Reacting particles must encounter each other.
Contact alone is not enough; the orientation must allow the relevant rearrangement.
A suitable collision also needs adequate energy. Not every collision produces a reaction.
See OpenStax Chemistry 2e: Collision Theory. The illustration does not assign measured energies to individual particles.
Formula & worked example
For k₁ = 0.001 s⁻¹ at 300 K and k₂ = 0.01 s⁻¹ at 330 K:
Eₐ ≈ 63,177.70 J/mol = 63.18 kJ/mol
Convert all temperatures to kelvin before calculating. For energy in eV, the value is per molecular event.
Frequently asked questions
Why must temperatures be in kelvin?
Arrhenius equations use absolute thermodynamic temperature. Celsius and Fahrenheit inputs are converted to kelvin before calculation; repeated unit changes do not recalculate from rounded display values.
Can activation energy be negative?
Yes, an empirical Arrhenius fit can have negative apparent activation energy. The fitted rate then decreases with increasing temperature. This is not a literal negative barrier on a conventional single-step potential-energy diagram.
Does the energy diagram determine ΔH?
No. ΔH is an independent illustrative input. The teaching profile places reactants, an assumed transition state and products relative to one another; it does not establish a mechanism or derive reaction enthalpy from two rate measurements.
Why is a two-point line not proof of Arrhenius behavior?
Two distinct measurements define a line exactly. They cannot test whether the relationship remains linear, establish a mechanism or quantify measurement uncertainty. More measurements and appropriate experimental analysis are needed.
What units should rate constants use?
Both measured rate constants must use the same compatible units, and A has those same units. The editable unit label does not perform a numerical conversion or change reaction order. The plot uses ln(k/k₀), with k₀ equal to one in those chosen units.
What does the temperature sweep show?
It evaluates the selected Arrhenius model at a changing temperature. It is not a simulation of individual molecular trajectories and does not predict reaction yield. Start and pause it manually; it also stops when the page is hidden or inputs change.
Sources & Reference Guides
Independent scientific references · no institutional endorsement or validation.
Explore temperature, reaction rates and the Arrhenius relationship.