Electrochemistry Lesson 5 Electrolytic Cells

Electrolysis Some reactions do not occur spontaneously – these reactions require energy input, and are called nonspontaneous reactions. In a galvanic cell, redox reactions are used to produce electrical energy, but the reverse is also possible. Electrical energy may be used to make a nonspontaneous redox reaction to occur. This process is called electrolysis. A cell in which electrolysis is occurring is called an electrolytic cell. The power supply acts as an “electron pump”, pushing electrons toward the cathode (and making it negatively charged) while pulling electrons away from the anode (and making it negatively charged). Positive ions in the solution move toward the cathode, where a reduction reaction occurs. Similarly, negative ions move toward the anode, where oxidation occurs. Without continuous electrical help from a power supply, the cell reactions would not occur.

Electrolysis (continued) An example would be the electrolysis of copper (II) chloride solution, using inert (nonreacting) graphite electrodes. The copper (II) chloride splits into positive copper ions and negative chloride ions. The copper ions move towards the cathode (because it is negatively charged), and the chloride ions move towards the anode (because it is positively charged). When the experiment is conducted, the familiar reddish colour of copper is observed at the cathode, and bubbles of green gas occur at the anode, thus you can assume that the reaction occurred

Galvanic and Electrolytic Cells (together) Commonly galvanic and electrolytic cells work together, like a rechargeable battery. For example, starting a car draws electricity from the battery, using up some of the chemicals in the battery. The battery would completely discharge if it weren’t for the car’s built-in recharger – the alternator. Once the engine is running, electrical energy from the alternator is pumped into the battery, where it is used to reverse the cell reaction. A car with a discharged battery requires an electrical boost from another vehicle to push the battery reaction in the reverse direction. Therefore, discharging occurs spontaneously and releases electrical energy, and recharging is nonspontaneous and requires electrical energy.