The Physical Meaning of Reversibility

It may be appropriate to ask here why the potential at a reversible electrode should change at all with current density. This does not occur because no system is really ideally polarizable , and one is observing a small polarization. Indeed the relationships shown in Eq. (4.20) holds strictly only when the interface is ideally nonpolarizable. 

When the above parameter is 10, the system can be considered to be essentially reversible. When it is 0.1 the system can be regarded as irreversible. 

Similar considerations can be used to determine reversibility in stirred solutions, for example, when measurement is conducted on a rotating disc electrode, where the Nemst diffusion layer is independent of time. 

This equation can be used to determine the values of feg h for which the reaction will behave reversibly for any rotationrate. We use the requirementthatfes,hS/D 0.1 for totally irreversible behavior and ks t b/D 10 for reversible behavior. For a rotation rate of 2500 rpm, for example, this leads to irreversible behavior for 3.4 X lO cms and reversible behavior for 3.4 x 10 cm s which 

A qualitative way of looking at reversibility is to consider the total overpotential as a sum of three terms 

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One should not be surprised to find that the distinction between so-called reversible and irreversible processes is not sharp and may depend on experimental conditions. The physical meaning of reversibility is that the concentrations of reactants and products at the... 

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