Application of ultramicroelectrodes in studies of homogeneous catalytic reactions—part III. The condition for quasi-first and second order homogeneous catalytic reactions at ultramicrodisk electrodes in the steady state

The conditions for quasi-first and second order homogeneous catalytic reactions and their variation with each other at an ultramicrodisk electrode in the steady state are discussed in this paper. The order of reaction can be controlled by changing the dimension of the ultramicroelectrode: the second order reaction can be changed to quasi-first by decreasing the dimension of the ultramicroelectrode. An example of this is given. The main factor effect on the reaction order is the dimension of the ultramicroelectrode. The K₄Fe(CN)₆-aminopyrine system is selected to confirm the theory, the experiments showing that the system is a second order reaction at a 432 μm microelectrode, and a quasi-first order reaction at a 19 μm ultramicroelectrode. The kinetic constant of the system can be determined by applying the previous theory of homogeneous catalytic reaction.