Kinetic laws of open systems with constant concentrations

Kinetic laws of open systems with constant concentrations 

In systems with concentrations that are held constant, the speeds with constant space function - which is the term ( ) of product SfE - are independent of time in isothermal conditions. This is true for the volumetric speed of a homogeneous system as well as for the areal speed of a catalytic system. This will be also true in the case of a strictly heterogeneous reaction that obeys the law of E. Space functions are, however, frequently a function of time, which leads to absolute speeds or to rates that vaiy with time through this space function. 

Finally we see that the real simplification in the resolution of systems is based on the existence of pseudo-steady state modes. It is the latter that enable us to replace the differential equations of intermediate balance with algebraic equations. Hence the interest in experimentally showing the adequacy introduced with experimental data. 

The notion of quasi-steady state, without being combined to a single and invariant volume, however, provides only little interest in itself in the end because it is not equivalent to the pseudo-steady state, which enables the true simplifications. 

We could have got along very well without the notion of quasi-steady state. We have stated this as the reader might cling to other books relating to kinetics that are too often, and wrongly, focused on the quasi-steady state, which implies that the volume or surface are invariant. The difference in volume and surface do, however, become paramount when mainly heterogeneous systems are tackled. 

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