Arrhenius Rate Constant Calculator
Calculate a reaction rate constant from the Arrhenius equation using activation energy and temperature.
How it works
k = A · e^(−Ea / (R·T)) · R = 8.314 J/(mol·K) · Ea entered in kJ/mol is converted to J/mol
The Arrhenius equation links a reaction's rate constant to temperature. A is the pre-exponential (frequency) factor, Ea the activation energy — the minimum energy a collision needs to react — and R the gas constant. The exponential term is the fraction of molecules with enough energy; it rises steeply with temperature, which is why warming a reaction speeds it up so dramatically.
Worked example
For A = 1×10¹³ s⁻¹, Ea = 50 kJ/mol and T = 298 K: the exponent is −50,000 ÷ (8.314 × 298) ≈ −20.18, so k = 10¹³ × e^(−20.18) ≈ 1.7×10⁴ s⁻¹.
Sources: Arrhenius equation — Wikipedia
Frequently asked questions
Why is activation energy in kilojoules but R in joules?
Activation energies are conventionally quoted in kJ/mol, while R is 8.314 J/(mol·K). The calculator multiplies Ea by 1,000 so both are in joules and the units cancel.
Why does a small temperature rise speed reactions so much?
Because temperature sits inside an exponential. A 10 °C rise near room temperature can roughly double or triple many rate constants, since more molecules clear the activation-energy barrier.
What is the pre-exponential factor A?
It reflects how often molecules collide with the correct orientation to react. It has the same units as k and is often found from experiment or the collision theory of the reaction.
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