The conduction of salt water is a chemical change. There are two types of conductors that are common in life, one is electronic conductors and the other is ionic conductors. Electron conductors rely on the movement of electrons to conduct electricity, and carriers include electrons and holes, such as metals, semiconductors, etc. Ionic conductors rely on ion mobility to conduct electricity, including electrolyte solutions (table brine), molten electrolytes, solid electrolytes, etc.
Taking the wires (including electrodes) and salt water of the external circuit of the power supply as the research object, it can be found that they contain both electronic conduction and ion conduction processes, and the chemical reaction occurs at the interface where the two are converted into each other. When electrons are conducted to the cathode, they cannot enter the water alone to conduct conduction, but will combine with hydrogen ions that migrate to the vicinity of the cathode under the action of the electric field, and the hydrogen ions get electrons and become hydrogen, and a reduction reaction occurs, from electron conduction to ion conduction. In the same way for the anode, chloride ions migrate to the anode under the action of an electric field, and the chloride ions lose electrons, and an oxidation reaction occurs to generate chlorine gas, and the lost electrons enter the anode to participate in conduction, and the ionic conduction changes to electronic conduction.
In short, after the ionic conductor and the electron conductor are connected in series, there must be electron gain and electron loss reactions at the interface of the two types of conductors, that is, electrochemical reactions must occur. This also brings us to the definition of electrochemistry: the science of studying the phenomenon of the charged interface formed by electron and ionic conductors and the changes that occur on them.
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