Well, if the reaction you are considering is rightly understood as a chemical change, then is most logical to consider the slowest step (the step with highest activation energy) as the rate determining step. You may find attached this for details.

Dear Kaana Asemave,

The solid state reaction kinetics are quite different from those of homogeneous kinetics. I am not sure whether the rate determining step is linked with activation energy in this case. Existing literature claims that diffusion or bond breaking stage at the surface of reaction is considered as the rate determining steps. But there is no explanation. I don't know whether these stages require high activation energy or not. Actually your answer is debatable and which will be excellent for enrichment of our understandings.

In case of a heterogeneous solid state reaction, one can not simply consider the step with higher activation energy as the rate limiting step. In fact, the currently kinetic evaluation methods are mainly based on Arrhenius function, which was established only for homogeneous gas phase chemical reaction. In the extensive literature concerned with the invention and the development of thermokinetic methods for experimental investigations of reaction rates and mechanisms, are the reported efforts to improve: (i) the accuracy and reliability of experimental techniques and apparatus, and (ii) the ability of mathematical/analytical methods to interpret kinetic data easily and rapidly from a minimum number of experiments. There has been many debates on this issue. However, the thing is that the distribution of energy in solids is not represented by the Boltzmann equation. The redistribution of vibrational energy within a crystalline phase differs from the mechanism of collisions between freely moving molecules, as envisaged in homogeneous reaction rate (Arrhenius) theory. In this case, you have to consider the inherent chemical background of your reaction, to figure out the possible decomposition mechanism by some other techniques including MS, FTIR, XRD. Be sure that all possible physical processes (melting, evaporation or sublimation et. al.) included in attempted reaction have been extensively considered, because they would significantly affect the apparent activation energy. On this basis, you may find out the rate limiting step of this reaction. I hope my comment would not confuse you.

Dear Qi-Long Yan,

Thank you for such an interesting answer which enrich my ideas about the solid sate reaction kinetics. But sir, is there any way to identify the rate determining step of a multistage decomposition reaction by simply interpreting the kinetic triplet (reaction model, activation energy and pre-exponential factor) ? In general the diffusion stage is considered as the rate determining stage for a solid state reaction . But if a solid sate decomposition reaction follows two different types of diffusion (say 'Avrami' and 'three dimensional diffusion -Jander type') reaction then how do I guess the rate determining step ?

Hi, Dr. Mostofa, I don't know what kind your reaction you are investigating, and hence I could not make any conclusion on the rate limiting step. Anyway, as you mentioned, the reaction model may tell you something. The model for different steps might be different, you can make a decision on that issue.

Dear Qi-Long-YAn

Sir, plese don't call me Dr. Mostofa. I have not completed my PhD yet. Right now i am pursuing it sir. I am studying the decomposition kinetics of Zn-Al NO3 LDH. We identified three distinct stages- first two stages follow an Avrami model and the last stage follows a three dimensional diffusion reaction model. I am little bit confused abut the rate determining step of that decomposition reaction.

As to the answer of M. Shamim: a reaction proceeds faster it the reaction rate is higher, not if the activation energy is lower. In the case of the Arrhenius equation, the reaction rate is determined not only by the activation energy, but also by the preexponential factor and the conversion function. Please, read my paper CONSIDERATIONS ON THE SINGLE-STEP KINETICS APPROXIMATION published in Journal of Thermal Analysis and Calorimetry, Vol. 82 (2005) 651–657.

Dear Peter Simon sir,

Your answer clear a lot of confusion of mine regarding solid state kinetics. The paper (and it's some interesting references also) you mentioned enrich my knowledge about the subject, specially the interesting discussion about the effect of pre exponential factor on reaction rate and hence activation  energy. Thank you sir for your answer. 

There are two types of solid state reactions involving the thermal decomposition and formation of the product from the reactants. Typical examples are thermal decomposition of CaCO3 and oxidation of metals and alloys respectively.The former involves bond breaking, charge transfer , formation of atoms and molecules at the interface between the reactants and the products followed by desorption.The slowest of these steps will be rate determining..The activation energy determined experimentally should correspond to one of these steps, such as that for breaking the bond or charge transfer etc. The reaction for oxide formation involves adsorbtion of oxygen molecules followed by dissociation to atoms, electron transfer to form oxygen and metal ions and diffusion of these ions through the oxide film.The experimentally determined activation energy would correspond to the slowest of these steps.The energies involved in the steps such as electron transfer, diffusion etc. are available in the literature for comparison.