Activation Energy Calculator
The activation energy calculator determines the energy barrier for a chemical reaction from experimental rate constant data at two temperatures. Activation energy (Ea) is the minimum kinetic energy reactant molecules must possess to successfully collide and form products. It determines how sensitive a reaction rate is to temperature changes: reactions with high Ea speed up dramatically when heated, while low-Ea reactions respond more weakly. This tool uses the linearized two-point form of the Arrhenius equation to calculate Ea from k1 at T1 and k2 at T2. It also computes the frequency factor A and predicts the rate constant at a third temperature if needed.
Activation energy formula
Ea = R * ln(k2/k1) / (1/T1 - 1/T2)
Arrhenius: k = A * exp(-Ea / (R*T))
R = 8.314 J/(mol*K)
T(K) = T(degC) + 273.15
Typical activation energies
- Enzymatic reactions in biology: 40 to 80 kJ/mol
- Acid-catalyzed reactions: 50 to 100 kJ/mol
- Uncatalyzed reactions: 100 to 250 kJ/mol
- Combustion: 125 to 200 kJ/mol
- Diffusion in solids: 50 to 200 kJ/mol
Activation energy: frequently asked questions
What is activation energy?
Activation energy (Ea) is the minimum energy that reactants must have to transform into products. It is the energy barrier that must be overcome for a chemical reaction to occur. Higher Ea means a slower reaction at a given temperature. Enzymes and catalysts work by lowering the activation energy, speeding up reactions without being consumed.
How is activation energy calculated from rate constants?
Using the two-temperature form of the Arrhenius equation: Ea = R * ln(k2/k1) / (1/T1 - 1/T2), where k1 and k2 are rate constants at temperatures T1 and T2 (in Kelvin), and R = 8.314 J/(mol*K). This can also be written as: ln(k2/k1) = (Ea/R) * (1/T1 - 1/T2).
What is the Arrhenius equation?
The Arrhenius equation is k = A * exp(-Ea / (R*T)), where k is the rate constant, A is the pre-exponential (frequency) factor, Ea is activation energy, R is the gas constant, and T is absolute temperature. Taking the logarithm: ln(k) = ln(A) - Ea/(R*T), which is linear in 1/T.
What does a high vs low activation energy mean?
High Ea (greater than 200 kJ/mol): reaction is slow at room temperature, significant temperature increase needed to speed it up (e.g., combustion of hydrocarbons). Low Ea (less than 40 kJ/mol): reaction is fast even at low temperatures (e.g., radical chain reactions, some acid-base reactions). Enzymes typically have Ea of 40 to 80 kJ/mol.
How does temperature affect reaction rate?
A useful approximation: for many reactions, the rate doubles with every 10 degC rise in temperature near room temperature. This corresponds to Ea of about 50 to 60 kJ/mol. More precisely, the Arrhenius equation shows the exponential relationship: a small increase in temperature provides many more molecules with enough energy to cross the activation energy barrier.
Official sources
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.