Arrhenius
Exponential dependence on 1/x. Use it for reaction rate constants, vapor pressures and other thermally activated quantities measured against absolute temperature.
Fit the example dataStart with your own data
Example: simulated rate constants of a first-order reaction between 290 and 350 K, 13 points with x and y uncertainties, opened as a new copy you can edit.
Parameters
- Pre-exponential factor: the value y approaches at very large x.
- Exponent coefficient, in the units of x. For a rate constant against absolute temperature, B = −Eₐ/R, where Eₐ is the activation energy and R the gas constant.
Tips
- Use absolute temperature, in kelvin, not degrees Celsius.
- Automatic starting values come from a straight line fitted to ln y against 1/x, so a blank Guess usually works. To start by hand, use that line’s slope for B and the exponential of its intercept for A.
- Fitting y itself, with δy where you have it, keeps each point’s own uncertainty; taking ln y changes how the points are weighted.