The pseudo-steady state mode test

To prove the pseudo-steady state mode, two methods are used to determine the reaction rate and the measured rate. The first method is simultaneously compared to the one measured by calorimetiy. 

Research into the uniqueness of the space function mechanism or test 

This test is carried out after the pseudo-steady state test, since it is only valid if the former is satisfied. 

The test aims to determine whether the rate measured is written as a product of a function of only physico-chemical variables (temperature, concentrations, partial pressure, etc.) by a function of the morphological characteristics of a medium (surface-to-volume ratio, area of interfaces, volumes of the phases, etc.). 

In homogenous kinetics the method is used to prove that there is only one way, without parallel ways, for the reaction to happen. This is no longer tme if a reaction occurs simultaneously within and on the walls of the reactor. 

We have seen that the modeling of the rate is largely facilitated by the assumption of pseudo-steady state modes. It is thus of the greatest utility to be able to verify or cancel this assumption by an experimental technique for each studied reaction. In addition, it is also interesting to know whether the rate is separable since this limits the number of modes to be considered. We will describe two experimental tests that make it possible to answer these two questions. 

We are going to base our measurement of the two experimental speed ratios on the speed ratio of the mass change and the calorimetric flow. 

We conclude that this ratio, in the ease of a pseudo-steady state mode [11.13], is independent of time. 

Remark- The enthalpy of the reaction must be calculated with the same stoichiometric numbers as those used for the mechanism of the total reaction. 

For the experiments, there exist commercial devices that combine the measurement of mass and heat flow two measurements are thus carried out simultaneously and under the same conditions. It is advisable to take the derivative of the mass change. These devices use gas flows controlled by mass flow meters located upstream and that allow fixing the partial pressures of various gases. 

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