Calculator Inputs
Choose a method and enter kinetic data to compute the pre-exponential factor.
Example Data Table
| Case | Method | Inputs | Calculated A | Notes |
|---|---|---|---|---|
| Example 1 | Direct | k = 0.012 s^-1, Ea = 55 kJ/mol, T = 25 °C | 5.185186e+7 s^-1 | Moderate frequency factor for a slower reaction. |
| Example 2 | Direct | k = 1.85 s^-1, Ea = 42 kJ/mol, T = 350 K | 3.429305e+6 s^-1 | Useful for comparing catalyst or solvent effects. |
| Example 3 | Two-point fit | k1 = 0.08 s^-1 at 300 K, k2 = 0.65 s^-1 at 330 K | 8.149802e+8 s^-1 | Estimated Ea is about 57.48 kJ/mol. |
Formula Used
Arrhenius equation: k = A × e-Ea / (R × T)
Rearranged for the factor: A = k × eEa / (R × T)
Two-point activation energy estimate:
Ea = R × ln(k2 / k1) ÷ [(1 / T1) − (1 / T2)]
- k = rate constant for the reaction.
- A = pre-exponential factor or frequency factor.
- Ea = activation energy.
- R = gas constant, 8.314462618 J mol-1 K-1.
- T = absolute temperature in kelvin.
How to Use This Calculator
- Select Direct Arrhenius mode when you already know k, Ea, and T.
- Select Two-point Arrhenius fit when you have rate constants at two temperatures.
- Enter the correct temperature units and activation energy units before calculating.
- Add a target temperature when you want the calculator to estimate a new rate constant.
- Click Calculate Factor to display results above the form.
- Use the export buttons to download the current result set as CSV or PDF.
FAQs
1. What does the pre-exponential factor represent?
It reflects how often reactant molecules collide successfully with the right orientation. In many systems, larger values suggest more frequent effective collisions.
2. Why must temperature be converted to kelvin?
The Arrhenius equation uses absolute temperature. Using Celsius or Fahrenheit directly would distort the exponent and produce incorrect kinetic results.
3. Does the factor always have units of s^-1?
No. Its units match the rate constant for the reaction order used. First-order reactions often use s^-1, but other orders use different units.
4. When should I use the two-point method?
Use it when activation energy is unknown but you have two reliable rate constants measured at different temperatures. It estimates Ea first, then calculates A.
5. Can catalysts change the pre-exponential factor?
Yes. Catalysts mainly lower activation energy, but they can also affect orientation, transition-state accessibility, and collision effectiveness, which may alter the factor.
6. Why does my result appear in scientific notation?
Frequency factors often span many orders of magnitude. Scientific notation keeps the output compact, readable, and easier to compare across reaction systems.
7. What causes a nonphysical activation energy warning?
It usually means the two rate constants and temperatures do not follow expected Arrhenius behavior, or the inputs were entered with incorrect values or units.
8. Can I use this for teaching and lab checks?
Yes. It is useful for classroom demonstrations, lab worksheet verification, kinetic comparisons, and quick sensitivity checks before deeper modeling.