Hi.

The approach is still based on the same principle, only can become more complex because of the reversibility. You still determine orders, energies and pre-exponential factors. It's not easy to present you with a short accurate "receipe", so I would recommend you to read Fogler's "chemical reaction engineering".

To start, this is also interesting: http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch22/react.html

Sometimes it's better to cover the theory and stop the experiment for some time. Good luck!

You can use the Arrhenius law in logarithm form to get the forward activation energy and forward rate frequency using only the ;lower temperature section of data.

Ln (k1) = Ln (A1) - E1/RT

The same equation can be used with the highest temperature section of data to get the reverse activation energy and backward frequency.

For exotherm the reverse activation energy should be higher than the forward activation energy.

Ln (k2) = Ln (A2) - E2/RT

There are many other equations that try to get all the data in one equation, but the results are about the same.

Conventionally you do it with the Arrhenius Plot, Ln(k) vs 1/T to get the values of pre-exponential factor from the intercept and activation energy from the slope.

As I understood, if your reaction is irreversible, there is not point in reduction of rate with temperature. The reduction in rate can be due to different things - 1. if catalytic reaction then deactivation rate is also enhanced with temperature and you don't see required rise in rate. 2. All products are not taken care while calculating conversion - some side products has formed - so in real, rate is high but not computed right.

If you can specify your system and method you used to get rate things will be clear and easy to help.

Reaction rate increases with increasing the reaction temperature. Well the TOF won't be only determined by Ea, but also coverage of surface species. For example, once you increase the reaction temperature to a certain level, the surface of the catalyst changed from a reactant covered surface to an empty surface, then the slope of the Arrhenius Plot could be revered as a function of reaction temperature.

Hopefully, that helps.

Good luck.

Reducing of the reaction rate with temperature indicates a highly exothermic slow step . Activation energy can be calculated using Arrhenius equation. By plotting

lnk versus 1/T will be straight line of positive slope were the activation energy can be calculated from the slope and frequency factor can be calculated from the intercept

Thanks for all the comments.

Alaa Eldin Mokhtar Abdel-hady you are correct.this reaction is a highly exothermic reversible reaction.

in this case I am having a arrhenius plot with two different slopes,one with negative slope in lower temperature region and one with positive slope(higher temperature region). so i am getting two activation energy.

Can i take an average of these two values? or should i use some sort of linear relationship to express these two values?

If you want to calculate the activation of the overall reaction( forward and backward reactions) you must take the average values which Known as enthalpy. If yo want to calculate the activation energy for the exothermic reaction only , this can be obtained from the plot of the positive slope of(ln k Versus 1/T). If you want to calculate the activation for the endothermic reaction ,this can be obtained from the plot of negative slope.

Yours Sincerely

Alaa Eldin Mokhtar Abdel-hady thanks for your comment.

Actually, i can see both negative and positive slope during exothermic reaction. i.e. i am getting a negative slope on arrhenius plot around lower temperature range(e.g. 100 to 150 C) and after that the reaction rate reduces and thereby getting a positive slope over a temperature(e.g.150-200).