How this calculation works
Prediction uses entered activation energy in kJ/mol, converts it to J/mol and applies the reciprocal-Kelvin difference. Inference solves the same two-point expression for apparent activation energy.
ln(k₂/k₁) = Ea / R × (1/T₁ − 1/T₂)A worked example
At T₁ 300 K, T₂ 310 K, k₁ 0.001 and Ea 50 kJ/mol, the constant-factor Arrhenius scenario predicts k₂ about 0.001909. The result retains the same units and reaction-order basis as k₁.
Good to know
Two-point constant-Ea scenario, not mechanistic proof or an extrapolation guarantee. Both constants need the same units and reaction-order convention. Kelvin required; no uncertainty propagation.
Reference: OpenStax: Arrhenius equation (opens in a new tab) ↗
Use absolute temperatures
The exponential relationship contains reciprocal temperature, so Kelvin is required. A ten-degree temperature increase is not enough information without the original absolute temperature.
Activation energy is entered in kilojoules per mole and converted once to joules per mole to match the gas constant. Missing that factor of one thousand creates a very different prediction.
The parent daughter decay chain calculator adds model a two-member decay chain with initial daughter, branching and stable or equal-half-life cases, showing expected inventories and unit-labeled activities. The integrated reaction order fit calculator adds compare zero-, first- and second-order integrated linear fits with original-concentration residuals, explicit transform limitations and a selected fitted curve.
Prediction and inference answer different questions
Prediction assumes an activation energy and computes a second rate constant. Inference uses two measured constants and estimates the apparent activation energy that connects those two points.
The rate constants must use consistent units and the same reaction-order convention. Two identical temperatures cannot identify activation energy and are rejected in inference mode.
A fitted slope does not establish a mechanism
The two-point model assumes a constant pre-exponential factor and activation energy over the temperature interval. More complex behavior can depart from that assumption even when two measurements fit exactly.
A negative apparent activation energy is returned rather than silently forced positive. It describes this fitted two-point relation and does not prove a simple elementary reaction pathway.
Use the result with the next measurement
The Nernst cell potential calculator also uses absolute temperature and a logarithm, but it relates equilibrium activities to potential rather than fitting reaction-rate constants.
Two-point constant-Ea scenario, not mechanistic proof or an extrapolation guarantee. Both constants need the same units and reaction-order convention. Kelvin required; no uncertainty propagation.
A few questions, answered
Can I enter Celsius directly?
No, both temperatures must be Kelvin.
Can inference return negative Ea?
Yes, the apparent two-point estimate is not forced positive.
Do the rate constants need matching units?
Yes, including the same reaction-order convention.