# Activation Energy Calculator (Arrhenius Equation)

Free activation energy calculator using the Arrhenius equation. Calculate Ea from rate constants at two temperatures. Step-by-step solutions.

## What this calculates

Calculate activation energy (Ea), rate constant (k), or temperature using the two-point Arrhenius equation: ln(k₂/k₁) = -(Ea/R)(1/T₂ - 1/T₁). Enter rate constants at two temperatures to find the activation energy.

## Inputs

- **Solve For** — options: Activation Energy (Ea), Rate Constant at T₂ (k₂), Temperature T₂ — Using the two-point Arrhenius form: ln(k₂/k₁) = -(Ea/R)(1/T₂ - 1/T₁).
- **Rate Constant k₁** — min 0 — Rate constant at temperature T₁.
- **Temperature T₁** (K) — min 0 — First temperature in Kelvin.
- **Rate Constant k₂** — min 0 — Rate constant at temperature T₂.
- **Temperature T₂** (K) — min 0 — Second temperature in Kelvin.
- **Activation Energy (Ea)** (kJ/mol) — min 0 — Activation energy (needed when solving for k₂ or T₂).

## Outputs

- **Result** — The calculated value.
- **Unit** — formatted as text — Unit of the result.
- **Arrhenius Calculation** — formatted as text — Step-by-step using the two-point Arrhenius equation.
- **Rate Increase Factor** — formatted as text — How many times faster the reaction is at T₂ vs T₁.

## Frequently Asked Questions

**Q: What is activation energy?**

A: Activation energy (Ea) is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to form products. Higher Ea means slower reactions.

**Q: What is the Arrhenius equation?**

A: The Arrhenius equation is k = A·exp(-Ea/RT), where k is the rate constant, A is the pre-exponential factor, Ea is activation energy, R is the gas constant (8.314 J/(mol·K)), and T is temperature in Kelvin.

**Q: How does a catalyst affect activation energy?**

A: A catalyst lowers the activation energy by providing an alternative reaction pathway. This speeds up the reaction without being consumed. The catalyst does not change ΔG or the equilibrium position.

**Q: What are typical activation energy values?**

A: Most chemical reactions have Ea between 40-200 kJ/mol. Enzyme-catalyzed reactions may have Ea as low as 10-30 kJ/mol. Very fast reactions (like explosions) have low Ea, while slow reactions (like rusting) have high Ea.

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Source: https://vastcalc.com/calculators/chemistry/activation-energy
Category: Chemistry
Last updated: 2026-04-21