REDOX REACTION EQUATIONS AND APPLICATIONS Overview of Redox Reactions: o Change in Oxidation State: Loses Electrons = Oxidized (Oxidation number increases) Gains Electrons = Reduced (Oxidation Number Reduced) o One substance must be reduced and one must be oxidized (electrons given off by one must be accepted by another similar to the law of conservation of energy which says that energy can never be created nor destroyed) o Identifying which species are oxidized and which are reduced can break net ionic equation into half reactions Net Equation: Cu (s) + 2 Ag + Cu 2+ + 2 Ag (s) Oxidized: Cu (s) Cu 2+ Reduced: 2 Ag + 2 Ag (s) Where do the electrons belong? o Electrons are written in half reactions but not in net ionic equations. Why? Well, let s see. Oxidized: Cu (s) Cu 2+ + 2 e - Reduced: 2 Ag + + 2 e - 2 Ag (s)
When the two half reactions are added together, the electrons cancel each other out and therefore do not appear in the net equation. Compare Oxidizing and Reducing Agents: Oxidizing Agent causes oxidation to occur in another species = species being reduced (gains electrons) Oxidizing agent is a thief that steals electrons o Strong Oxidizing agent is a species that strongly attracts electrons Reducing Agent causes reduction to occure in another species = species being oxidized (loses electrons) Reducing agent has electrons taken from it. o Strong Reducing agent is a species that does not hold its electrons very tightly BATTERIES: what causes a battery to give off electricity? o Chemical energy is converted to electrical energy by means of a redox reaction. o SHOW PICTURE OF BATTERY (common electrochemical cell) o Electrochemical Cell a cell that either converts chemical energy into electrical energy or converts electrical energy into chemical energy by a redox reaction.
o Label: Voltaic Cell: A redox reaction in which electrons pass through an external circuit rather than directly from one substance to another. Cathode: electrode where reduction occurs Anode: electrode where oxidation occurs Electrode: a solid chemical conductor in a cell where the electrical connections are made, the site of oxidation and reduction Electrolyte: A solution that conducts an electric current. Reduction (copper) Oxidation (zinc)
Oxidizing Agent - copper Reducing Agent - zinc Salt Bridge a tube or connection containing an electrolyte that connects two half cells Flow of electrons anode to cathode Voltmeter a device used to measure electric potential difference in Volts Volt measure of the tendency to do electrical work Another way to write reaction: Cu (s) Cu 2+ (aq) Zn 2+ (aq) Zn (s) Cathode (+) Electrolyte Electrolyte Anode (-) Reduction Oxidation = interface between electrode and electrolyte = porous boundary between half cells (salt bridge) Example: Potato with zinc and copper o Potato has phosphoric acid o Same redox reaction as above occurs and chemical energy is converted to electrical energy
CORROSION as an example of redox Read section 15-8 on pg 329-330 Overview of Redox Reactions: o Change in Oxidation State: Loses Electrons = Oxidized (Oxidation number increases) Gains Electrons = Reduced (Oxidation Number Reduced) o One substance must be reduced and one must be oxidized (electrons given off by one must be accepted by another similar to the law of conservation of energy which says that energy can never be created nor destroyed) o Identifying which species are oxidized and which are reduced can break net ionic equation into half reactions Net Equation: Cu (s) + 2 Ag + Cu 2+ + 2 Ag (s) Oxidized: Cu (s) Cu 2+ Reduced: 2 Ag + 2 Ag (s) Where do the electrons belong? o Electrons are written in half reactions but not in net ionic equations. Why? Well, let s see. Oxidized: Cu (s) Cu 2+ + 2 e -
Reduced: 2 Ag + + 2 e - 2 Ag (s) When the two half reactions are added together, the electrons cancel each other out and therefore do not appear in the net equation. Compare Oxidizing and Reducing Agents: Oxidizing Agent causes oxidation to occur in another species = species being reduced (gains electrons) Oxidizing agent is a thief that steals electrons o Strong Oxidizing agent is a species that strongly attracts electrons Reducing Agent causes reduction to occure in another species = species being oxidized (loses electrons) Reducing agent has electrons taken from it. o Strong Reducing agent is a species that does not hold its electrons very tightly BATTERIES: what causes a battery to give off electricity? o Chemical energy is converted to electrical energy by means of a redox reaction. o SHOW PICTURE OF BATTERY (common electrochemical cell) o Electrochemical Cell a cell that either converts chemical energy into electrical energy or converts electrical energy into chemical energy by a redox reaction.
o Label: Voltaic Cell: A redox reaction in which electrons pass through an external circuit rather than directly from one substance to another. Cathode: electrode where reduction occurs Anode: electrode where oxidation occurs Electrode: a solid chemical conductor in a cell where the electrical connections are made, the site of oxidation and reduction Electrolyte: A solution that conducts an electric current. Reduction (copper) Oxidation (zinc)
Oxidizing Agent - copper Reducing Agent - zinc Salt Bridge a tube or connection containing an electrolyte that connects two half cells Flow of electrons anode to cathode Voltmeter a device used to measure electric potential difference in Volts Volt measure of the tendency to do electrical work Another way to write reaction: Cu (s) Cu 2+ (aq) Zn 2+ (aq) Zn (s) Cathode (+) Electrolyte Electrolyte Anode (-) Reduction Oxidation = interface between electrode and electrolyte = porous boundary between half cells (salt bridge) Example: Potato with zinc and copper o Potato has phosphoric acid o Same redox reaction as above occurs and chemical energy is converted to electrical energy
CORROSION as an example of redox Read section 15-8 on pg 329-330