Redox in Electrochemistry Electrochemistry is the study of the redox processes by which chemical energy is converted to electrical energy and vice versa. Section 20-1

Redox in Electrochemistry (cont.) A salt bridge is a pathway to allow the passage of ions from one side to another, so that ions do not build up around the electrodes. An electrochemical cell is an apparatus that uses a redox reaction to produce electrical energy or uses electrical energy to cause a chemical reaction. Section 20-1

Redox in Electrochemistry (cont.) A voltaic cell is a type of electrochemical cell that converts chemical energy to electrical energy by a spontaneous redox reaction. Section 20-1

Chemistry of Voltaic Cells An electrochemical cell consists of two parts called half-cells, in which the separate oxidation and reduction reactions take place. The electrode where oxidation takes place is called the anode. The cathode is the electrode where reduction occurs. Section 20-1

Calculating Electrochemical Cell Potentials The tendency of a substance to gain electrons is its reduction potential. Section 20-1

Calculating Electrochemical Cell Potentials (cont.) The standard hydrogen electrode consists of a small sheet of platinum immersed in a hydrochloric acid solution that has a hydrogen ion concentration of 1 M. Hydrogen gas (H2), at a pressure of 1 atm, is bubbled in and the temperature is maintained at 25°C. Section 20-1

Calculating Electrochemical Cell Potentials (cont.) Formula for cell potential E0cell = E0reduction – E0oxidation Section 20-1

End of Section 20-1

Dry Cells A battery is one or more voltaic cells in a single package that generates electric current. Section 20-2

Dry Cells (cont.) A dry-cell is an electrochemical cell in which the electrolyte is a moist paste. The paste in a zinc-carbon cell consists of zinc chloride, manganese(IV) oxide, ammonium chloride, and a small amount of water. Section 20-2

Dry Cells (cont.) Primary batteries produce electric energy by means of redox reaction that are not easily reversed. Secondary batteries depend on reversible redox reactions and are rechargeable. Section 20-2

Fuel Cells A fuel cell is a voltaic cell in which the oxidation of a fuel is used to produce electric energy. Section 20-2

Fuel Cells (cont.) How a fuel cell works Potassium hydroxide is often the electrolyte. The oxidation half reaction 2H2(g) + 4OH– → 4H2O + 4e– The reduction half reaction O2(g) + 2H2O(l) + 4e– → 4OH–(aq) When combined, the equation is the same as burning hydrogen in oxygen to form water. Section 20-2

Corrosion Corrosion is the loss of metal resulting from an oxidation-reduction reaction of the metal with substances in the environment. Section 20-2

Galvanization is the process of coating iron with a layer or zinc. Corrosion (cont.) Galvanization is the process of coating iron with a layer or zinc. Section 20-2

End of Section 20-2

Reversing Redox Reactions The use of electrical energy to bring about a chemical reaction is called electrolysis. An electrochemical cell in which electrolysis occurs is called an electrolytic cell. Section 20-3

Applications of Electrolysis (cont.) Objects can be electroplated with a metal such as silver. The cathode is the object to be electroplated, where reduction occurs. The anode is a bar of silver, where silver is oxidized and silver ions transferred to the cathode. Section 20-3