Activation Energy Calculator
Activation energy from two rate constants at two temperatures — or the rate change a temperature shift will cause.
The Arrhenius equation k = A e^(−Ea/RT) links rate to temperature.
How the activation energy calculator works
The Arrhenius equation k = A e^(−Ea/RT) links rate to temperature. Measured at two temperatures, it rearranges to Ea = R ln(k₂/k₁) / (1/T₁ − 1/T₂).
The exponential is what makes reactions so temperature-sensitive: a typical activation energy of 50 kJ/mol means the rate roughly doubles for every 10 °C, which is the origin of that rule of thumb.
Formula: Ea = R ln(k₂/k₁) / (1/T₁ − 1/T₂)
Worked examples
| Inputs | Result | Note |
|---|---|---|
| Rate doubles from 25 to 35 °C | 52.9489 | Ea ≈ 52.9 kJ/mol |
| Predict the rate at 45 °C | 3.8344 | about four times |
| A slower-responding reaction | 13.9274 | a much lower activation energy |
FAQFrequently asked questions
What is activation energy?
The energy barrier a reaction must climb. A higher barrier means fewer molecules have enough energy at a given temperature, so the reaction is slower.
Why does the rate double every 10 °C?
It is a rule of thumb that holds for activation energies around 50 kJ/mol near room temperature. Reactions with higher barriers are more temperature-sensitive than that.
How do I measure it?
Measure the rate constant at two or more temperatures and apply the Arrhenius equation. A plot of ln k against 1/T gives −Ea/R as its slope.
Does a catalyst change it?
Yes — that is precisely what a catalyst does. It provides a lower-energy path, which is why small amounts have such large effects.
What is the pre-exponential factor?
A, roughly the collision frequency with the right orientation. It is the rate the reaction would reach if every collision succeeded.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.