Kinetics of Non-pseudo-steady State Modes

So far we have concentrated on the study of reactions occurring in a pseudosteady state mode. Obviously, such a state mode cannot exist throughout the entire reaction. At the beginning of the reaction, the amount of intermediate species starting from zero value must increase. Similarly, at the end of the reaction, for these quantities to become zero they must decrease. During both periods the state is not pseudo-steady as the reaction takes place in the transitory state. 

For many reactions, these two periods are short enough, with only very small variations in the extent of the reaction, to be neglected. 

In some cases, however, these transitory periods carmot be neglected and a kinetic law that does not correspond to the one deduced with the pseudo-steady state is observed for a significant reaction extent, even if the state tends toward a pseudosteady state. We will study the example of the paralinear law, which is sometimes obtained during the oxidation of metal plates. 

Finally, other reactions are such that they can never reach the pseudo-steady state mode. This is hue of those that lead to explosions or ignition. We will see the two classes of systems that can be attributed to these reactions thermal explosions and branched chain reactions with a positive branching factor. 

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Kinetics of Non-pseudo-steady State Modes 401 We see that this mean length is infinite for given values of pm and fra if ... 

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