Formal Kinetics Description of Chemical Reactions

The velocity of reactions in principle depends on the number of collisions per unit of time between the reactants. It may be assessed with the methods of physical chemistry. Yet, for practical applications it is determined experimentally. The experimental results are then evaluated using simplified model concepts. For this reason we speak of formal kinetics. 

A relatively general representation of the rate of reaction of homogeneous gas and liquid reactions is 

For heterogeneously catalyzed reactions Eq. (3.1) is used as well. Besides the following relationship is employed 

The dependence of the rate constant on temperature is crucial for safety considerations. It is described by the Arrhenius equation 

3) kp is the pre-exponential factor with the same unit as the rate constant, E the apparent energy of activation in J/mol, R the universal gas constant and T the absolute temperature. 

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