The document discusses oxidation-reduction (redox) reactions. It defines oxidation as loss of electrons and reduction as gain of electrons. Redox reactions involve the transfer of electrons between reactants. Oxidation numbers are used to identify oxidized and reduced species in redox reactions. Redox equations can be balanced using two methods - comparing oxidation number changes or using half-reactions. Electrochemical cells use spontaneous redox reactions to generate electricity, with oxidation occurring at the anode and reduction at the cathode.

1. CHAPTER 20 “ Oxidation-Reduction Reactions” LEO SAYS GER

9. Oxidation and Reduction (Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:

10. LEO says GER : L ose E lectrons = O xidation Sodium is oxidized G ain E lectrons = R eduction Chlorine is reduced

11. LEO says GER : - Losing electrons is oxidation, and the substance that loses the electrons is called the reducing agent . - Gaining electrons is reduction, and the substance that gains the electrons is called the oxidizing agent . Mg (s) + S (s) -> MgS (s) Mg is oxidized : loses e - , becomes a Mg 2+ ion S is reduced : gains e - = S 2- ion Mg is the reducing agent S is the oxidizing agent

13. Not All Reactions are Redox Reactions - Reactions in which there has been no change in oxidation number are NOT redox reactions. Examples:

38. Basic Concepts of Electrochemical Cells

42. Basic Concepts of Electrolytic Cells

45. End of Chapter 20