Chemistry (Chang), 9th Edition

Chapter 19: Electrochemistry

Chapter Summary

1. Redox reactions involve the transfer of electrons. Equations representing redox processes can be balanced using the ion-electron method.

2. All electrochemical reactions involve the transfer of electrons and therefore are redox reactions.

3. In a galvanic cell, electricity is produced by a spontaneous chemical reaction. Oxidation and reduction take place separately at the anode and cathode, respectively, and the electrons flow through an external circuit.

4. The two parts of a galvanic cell are the half-cells, and the reactions at the electrodes are the half-cell reactions. A salt bridge allows ions to flow between the half-cells.

5. The electromotive force (emf) of a cell is the voltage difference between the two electrodes. In the external circuit, electrons flow from the anode to the cathode in a galvanic cell. In solution, the anions move toward the anode and the cations move toward the cathode.

6. The quantity of electricity carried by 1 mole of electrons is called a faraday, which is equal to 96,500 C.

7. Standard reduction potentials show the relative likelihood of half-cell reduction reactions and can be used to predict the products, direction, and spontaneity of redox reactions between various substances.

8. The decrease in free energy of the system in a spontaneous redox reaction is equal to the electrical work done by the system on the surroundings, or ΔG = -nFE.

9. The equilibrium constant for a redox reaction can be found from the standard electromotive force of a cell.

10. The Nernst equation gives the relationship between the cell emf and the concentrations of the reactants and products under non-standard-state conditions.

11. Batteries, which consist of one or more galvanic cells, are used widely as self-contained power sources. Some of the better-known batteries are the dry cell, such as the Leclanché cell, the mercury battery, and the lead storage battery used in automobiles. Fuel cells produce electrical energy from a continuous supply of reactants.

12. The corrosion of metals, such as the rusting of iron, is an electrochemical phenomenon.

13. Electric current from an external source is used to drive a nonspontaneous chemical reaction in an electrolytic cell. The amount of product formed or reactant consumed depends on the quantity of electricity transferred at the electrode.