1. Reduction Oxidation and Potentials

2. Definitions Reduction – The process of an atom or ion becoming more negatively charged –They gain electrons (which are negative) –The term came from metals oxides being “reduced” to their “base” metals Fe 3+ + 3 electrons  Fe 0 Cl 2 + 2 electrons  2 Cl 1-

3. Definitions Oxidation – The process of an atom or ion becoming more positively charged –They lose electrons –The term came from what happens to most chemicals when they combine with oxygen 4 Fe + 3 O 2  2 Fe 2 O 3 Fe 0  Fe 3+ + 3 electrons S 4+  S 6+ + 2 electrons

4. Definitions Redox – Every chemical reaction that has a reduction must include an oxidation. If one atom is gaining electrons, another atom must be giving them off. –If the entire reaction is reversed, then so is the reduction and oxidation –For analysis the reactions can be separated, but a complete analysis will include both.

5. Consider the reaction: Iron + Sulfur  Iron Sulfide –Fe is oxidized ( Fe 0  Fe 2+ + 2 electrons) –S is reduced ( S 0 + 2 electrons  S 2- ) –The electrons are transferred from the iron (iron loses e, oxidized) to the sulfur (sulfur gains e, reduced) Fe + S  FeS A Redox Reaction Fe + S  FeS

6. Reversal of Redox The Reaction can be completely reversed: FeS  Fe + S –S is oxidized ( S 2-  S 0 + 2 electrons) –Fe is reduced ( Fe 2+ + 2 electrons  Fe 0 ) –The electrons are transferred from the sulfur to the iron FeS  Fe + S

7. Potential Electron Potential is measured in Volts Volts is a measure of the energy of each electron being transferred In a chemical reaction, the potential voltage measures the energy with which one atom loses an electron and another gains it. The voltage in NOT affected by the number of electrons.