# Arrhenius Model for Testing CD-R Media

by Dr. Brian J. Bartholomeusz

Technical Marketing, Writable CD Products

© 1995 Eastman Kodak Company

Used with permission

The Arrhenius model is used to describe the kinetics of an activated process. This assumes that an energy barrier hinders the forward progress of a reaction (degradation, corrosion, oxidation, etc.). The height of this energy barrier is, in a sense, the measure of the resistance to corrosion, for example. In order for the reaction to progress forward, a supply of an activation energy is required to surmount this barrier.

The rate at which the reaction proceeds depends on the impetus that is provided to surmount the activation energy barrier. This impetus commonly takes the form of heat and/or humidity. We therefore conduct experiments at different temperatures, and assuming that the energy barrier is constant, are able to determine its characteristics. We now know the barrier that must be surmounted to effect change and can therefore estimate what the rate of progress of the reaction at (say) room temperature.

In its simplest form, the Arrhenius model assumes that:

Rate of change is proportional to exp(-Ea/kT) |

exp represents exponential |

Ea is the activation energy |

k is the Boltzmann constant, or rate constant (an invariant physical parameter) |

T is the absolute temperature (temperature in degrees Kelvin) |

As you can see, increasing the temperature speeds up the rate of change.

What is the Arrhenius Model?

The Arrhenius Model is an excellent tool for exploring the relationship between activation energy and the speed of a chemical reaction. This equation has many scientific uses including calculating the rate of decay of a CD-R disc. The equation takes its name from Svante Arrhenius, the Swedish chemist who first explored the idea of activation energy in a reaction.

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