Dear Rajeev,

the answer to your question is no. There are several kinds of relaxation processes that do not follow the Arrhenius law. For example, the magnetic relaxation in spin glasses and in some magnetic nanoparticles systems is well described by using the Vogel-Fulcher law (E.g. see: S. Shtrikman, E.P. Wohlfarth, The theory of the Vogel-Fulcher law of spin glasses, Physics Letters A, Volume 85, Issues 8–9, 19, Page 467 (1981).)

Emphatically no. It is an approximation. The Eyring equation, which is similar to but not identical with the Arrhenius equation describes fairly well a single unimolecular reaction or a single bimolecular one - but such processes are VERY rare. Most processes can be described by a fairly complicated MECHANISM, a set of elementary reactions that can be descried by the Eyring theory. They are related by a kinetic matrix. The temperature dependence of the resultant energy MAY BE described by the Arrhenius equation if there is a single rate determining process (which is sometimes tha case with consecutive reactions in the stationary state). This is the problem of accelerated aging tests, where various conditions may acclerate processes which are aboslutely irrelevant under the normal conditions. The Arrhenius approximation is surely wrong if there is a phase transition between the original and the accelerated process. This even true for a glass transition which is not a (first order) phase tranisition. E.g the temperature dependence of relaxation processes can be approximately described by the Arrhenius picture below Tg and by other (nonlinear) equations above it. Nevertheless thw Arrhenius apporximation is widely used if there is nothing else or if we do not know the mechanism. In such cases, however, one should be very careful in giving a molecular interpretation to the activation energy.

Dear Rajeev,

the answer to your question is no. There are several kinds of relaxation processes that do not follow the Arrhenius law. For example, the magnetic relaxation in spin glasses and in some magnetic nanoparticles systems is well described by using the Vogel-Fulcher law (E.g. see: S. Shtrikman, E.P. Wohlfarth, The theory of the Vogel-Fulcher law of spin glasses, Physics Letters A, Volume 85, Issues 8–9, 19, Page 467 (1981).)

Dear Gyorgy Banhegyi and Walter Folly ·

Thank you for the information.

regards.

Most ceramics exhibit negative temperature coefficient behaviour, which is governed by an Arrhenius equation over a wide range of temperatures:

R=A*exp{B/T}

where R is resistance, A and B are constants, and T is absolute temperature (K).

Thank you very much Dr.Beliayev.

I agree fullt with the answers given but what like to add also the following;

1) Thermal fluctuations play the crucial role, ie the phenomena must be controlled by thermal activation.

2) The rate of a reaction itself does not generelly obey the Arrhenian behaviour because the thermodynamic driving force has a different temperature dependence.

Thank you John Agren.

I agree with what is said by Walter Folly, i.e, not always.

However, If a zero order kinetics is assumed for the beginning of a reaction (for example a thermo-oxidation, in which parallel reactions are not expected in the exact moment it starts), it will be possible to assume that the rate of reaction is done by the rate constant k. Thus, it is possible to construct an Arrhenius plot, However, the results should be evaluated carefully, using replicates for each temperature and a significant number of points (different temperatures). The reliability of the determined values should be confirmed by an uncertainty analysis (regression analysis). Finally, a comparison between the estimated values and literature values may turn possible to validate the findings.

Curvature may result from competing reactions or several critical reactions with individual temperature dependence within a more complex reaction scheme. If the range of temperatures studied is wide and overlap the glass transition temperature of the studied polymer, problems associated with curvature should also be considered and it will be better to plott correlations before and after the transition temperature.

Thank you Pimentel Real for the additional information.

Regards.

In the development of heat and mass transfer model for wood composite, we use the Arrhenius equation for predicting the curing behavior of urea formaldehyde. It is a temperature dependent property, so my answer is Yes, we can use it. For further details you can check my paper "Development of heat and mass transfer model for MDF". In another modelling work, Arrhenius equation is used to predict the curing behavior of plastic, that is also a temperature dependent property.

It is not very accurate, but with some approximation it is very useful. I have used it in the cement hydration process. Some applications are 'maturity function' of concrete, semi-adiabatic calorimeters and assessment of wood-cement compatibility. Please refer:"Assessment of wood-cement compatibility: A new approach" DOI:10.1515/HF.2003.101.

Look into W. Stiller: Arrhenius Equation and Non-Equilibrium Kinetics (just google it)

Thank you Prof.Balabas for the reference.

Whilst there are some exceptions (as pointed out above), many temperature dependent processes follow Arrhenius behaviour. Even in quantum mechanics the Arrhenius Law still holds and we use Arrhenius Law to model quantum tunnelling in single molecule magnets. It always seemed strange to me that this worked so well until I understood the origin of the equation in physical terms:

The Arrhenius Law assumes a Boltzman distribution of energy states e(-E/RT). This exponential term falls in the region 0 to 1 and effectively acts as a probability of the molecule having enough energy (E) to undergo the reaction.

The Arrhenius equation fails when (i) we have a system which does not follow standard Boltzman energy distributions i.e. has a non-equilibrium distribution of energies; (ii) when -E/RT is not constant, e.g. in an exothermic process, heat is evolved so (unless steps are employed to keep the temperature constant) the temperature increases. As T changes so does the term e(-E/RT).....so your reaction would speed up (or slow down for an endothermic process).

Dear Jeremy Rawson,

Simple,excellent and very useful. Thanks.