Kinetic Factors in Pyrolytic Chemical Reactions

In order to understand better the problems related to kinetic factors in pyrolytic reactions, a few basic concepts will be reviewed. The reaction rate of a chemical process where R is a reactant and P is a product is defined as the variation of the concentration of R or of P versus time. The reaction rate can be expressed by the relation  

This type of reaction is of the first order. The constant k is the rate constant. Concentrations are commonly expressed in mol / L, and k is expressed in s . The rate constant k is temperature dependent and it is a constant only in isothermal conditions. 

It is possible that the rate of reaction depends on the concentrations of the A and B species simultaneously. In this case the dependence is given by 

Some chemical reactions have a reaction rate of the form  

In order to understand how the constant k depends on temperature, it was assumed that the chemical reactions may take place only when the molecules collide. Following this collision, an intermediate state called an activated complex is formed. The reaction rate will depend on the difference between the energy of the reactants and the energy of the activated complex. This energy E is called activation energy (other notation E ). The reaction rate will also depend on the frequency of collisions. Based on these assumptions it was shown (e.g. [3]) that k has the following expression (Arrhenius reaction rate equation)  

---