Oxidation-Reduction Reactions. Electrolysis

The battery acts as an electron pump, pushing electrons into the cathode, C, and removing diem from the anode, A. To maintain electrical neutrality, some process within the cell must consume electrons at C and liberate them at A. This process is an oxidation-reduction reaction when carried out in an electrolytic cell, it is called electrolysis. At the cathode, an ion or molecule undergoes reduction by accepting electrons. At the anode, electrons are produced by the oxidation of an ion or molecule. 

If a chemical reaction can make electricity it should not be surprising to learn that electricity can make a chemical reaction. Using an electric current to cause a chemical reaction is called electrolysis, a technique widely used to win elements from their compounds. For example, pure sodium metal (Na) and chlorine gas (CI2) are obtained by passing electricity through molten sodium chloride (NaCl). The study of the interplay of electricity and oxidation-reduction reactions is called electrochemistry. 

These laws (determined by Michael Faraday over a half century before the discovery of the electron) can now be shown to be simple consequences of the electrical nature of matter. In any electrolysis, an oxidation must occur at the anode to supply the electrons that leave this electrode. Also, a reduction must occur at the cathode removing electrons coming into the system from an outside source (battery or other DC source). By the principle of continuity of current, electrons must be discharged at the cathode at exactly the same rate at which they are supplied to the anode. By definition of the equivalent mass for oxidation-reduction reactions, the number of equivalents of electrode reaction must be proportional to the amount of charge transported into or out of the electrolytic cell. Further, the number of equivalents is equal to the number of moles of electrons transported in the circuit. The Faraday constant (F) is equal to the charge of one mole of electrons, as shown in this equation ... 

An oxidation-reduction reaction that is not spontaneous, for which the calculated cell potential is negative, may be induced by electrolysis. This reaction can be due to an external electrical potential to force electrons into the couple undergoing reduction and to extract electrons from the couple undergoing oxidation. The minimum external potential required for electrolysis is the value of the calculated cell potential for the reaction. 

Electrolysis. The process whereby an electric current passes through a substance to cause a chemical change produces an oxidation-reduction reaction. 

Oxidation reduction reactions occur at two electrodes. The electrode at which oxidation occurs is called the anode the one at which reduction takes place is called the cathode. Electricity passes through a circuit under the influence of a potential or voltage, the driving force of the movement of charge. There are two different types of interaction of electricity and matter. Electrolysis is when an electric current causes a chemical reaction. Galvanic cell action is when a chemical reaction causes an electric current, as in the use of a battery. 

Special information about the electrode reactions is often needed in order to calculate the equivalent mass for electrolysis, just as in ordinary oxidation-reduction reactions. If a solution containing Fe " is electrolyzed at low voltages, the electrode reaction for the iron might be... 

Oxidation-reduction reactions are the basis of the branch of chemistry called electrochemistry. Such a reaction may occur spontaneously and produce electrical energy, as in a galvanic cell. If the reaction does not occur spontaneously, the addition of electrical energy may initiate a chemical change, a process called electrolysis. 

Chemical reactions that are unfavorable can be forced to proceed by the input of energy, as in the recharging of a secondary battery. Electrolysis reactions are oxidation-reduction reactions driven by electrical energy from an external power supply. Where electrons flow into the cell, the electrode becomes negatively charged, positive ions in solution migrate toward that electrode, and reduction takes place. In this type of cell (Figure 10.7), the electrodes need not be in separate compartments. 

In any electrochemical system, there are two electrodes, an anode and a cathode. During electrolysis, electrons are consumed at the cathode while they are generated at the anode. The reactions occurring at the individual electrodes are usually called the component electrochemical reactions, the combination being termed a redox, or oxidation-reduction, reaction system. Let us now examine the component electrochemical reactions involved in the overall reaction. 

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