Hi,
I have a question regarding modified Arrhenius equation:
k=ATbexp−E/RT
Does anyone knows how to choose the term temperature exponent 'b' for a specific reaction. The only thing I can find in literature is that it is often taken zero. But I can see it has effect on reaction results but could not find any literature to see how to choose it.
Many thanks in advance!
Dear Shahid,
By putting b to zero, you simply degenerate the modified Arrhenius to Arrhenius equation. The temperature dependency of the exponential factor is to give a better fit to an experimental observation. In that case it can be determined by fitting the equation to the experimental data.
Start at 0 and adjust to minimize the error in your data stepwise using an adjustment for -1 to 1 in increments of .01 with a spreads sheet might reveal an area where this adjustment is usefull. You should also check if a small adjustment to Ea and/or A works as well or better.
Only add the aditional variable if it significantly improves the data fit. In most cases it will not.
Temperature term is used to fit rate data with experimental data as ali mentioned. You may use curve fitting tools like kaleidagraph for this purpose.
This term results from the collision theory and is usually omitted in the calculations. The exponential function better reflects the influence of temperature on the rate of the chemical reaction than the power function. In addition, the inclusion of such a term may falsify the value of activation energy (possible numerical correlation between E and b). Regards,
Take the logarithm of the equation and fit your data to get the constants.
True, but only in case of a few experiments carried out at constant temperature. Regards,
b = 0 is common in the Arrhenius Theory. But there are other theories suggests different values for b. For more details, you can refer this paper.
https://doi.org/10.1002/aic.11775
i think it doesn't matter because the factor of temperature is considered in the Arrhenius equation as originally form and the frequency of collisions (A) is enough to time in the e -Ea/RT and you can apply your data of experiments with out any delaying
therefore they consider the exponent (b) mostly as zero.
In such scenario of modified constant, the unit of k changes. should we consider the unit of T^n or ignore it?
If we take photo induced electron transfer as an example, than we see that the full Marcus equation for electron transfer has a square root of T in the pre-exponential factor, below the line.
So for this process, "n = -0.5" is appropriate for the modified Arrhenius equation.
(because than it becomes a "simplified Marcus equation").
You can get rid of the unit of T^n by specifying the rate at one T.
Hi All,
If I'm doing simultaneous thermal and mechanical aging for a cable sample. How can I calculate the parameters, sigma and gamma of Zhukov equation?
Thanks
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