ELECTROCHEMISTRY. Lesson 1 Introduction to Redox

Transcription

1 ELECTROCHEMISTRY Lesson 1 Introduction to Redox

2 Electrochemistry generating electricity by harnessing a spontaneous chemical reaction OR using electricity to force a chemical reaction to occur (one that is non-spontaneous) Understanding electrochemistry requires a basic understanding of the processes called oxidation and reduction.

3 REDOX = Reduction + Oxidation The historic definitions: REDUCTION: reducing the volume of a naturally occuring metal ore (ie. CuO (s) ) into it s components and extracting the metal (ie. Cu (s) )

4 REDOX = Reduction + Oxidation The historic definitions: REDUCTION: reducing the volume of a naturally occuring metal ore (ie. CuO (s) ) into it s components and extracting the metal (ie. Cu (s) )

5 REDOX = Reduction + Oxidation The historic definitions: OXIDATION: The reaction of a metal with oxygen in the air, resulting in corrosion. These definitions are still somewhat true, but not nearly detailed enough for us!

6 Let s Investigate Obtain a piece of copper wire and a test tube of silver nitrate solution. Coil the wire around your pen and form a hook on one end. Hang the coil it over the edge of the test tube so the coil is covered by the solution. Observe over the course of the next few minutes and then again at the end of the lesson.

7 Let s Investigate 2Ag + + Cu 2Ag + Cu 2+

8 Tracking Oxidations and Reductions It can be hard to determine whether oxidation or reduction is occurring. A simple number line can sometimes help.

9 Oxidation Losing electrons 2Ag + + Cu 2Ag + Cu 2+ Gaining electrons Reduction

10 Oxidation means loss of electrons LEO Loss Electrons Oxidation Oxidation Half Reactions show how Metals or Anions lose electrons Balance charge 0 +2 Add electron to Cu Cu e - most positive side atom cation Oxidation-electrons are on the right

11 Oxidation means loss of electrons LEO Loss Electrons Oxidation Oxidation Half Reactions show how Metals or Anions lose electrons Balance charge -2 0 Add electron to 2 O 2- O 2 + 4e - most positive side anion atom Oxidation-electrons are on the right

12 Reduction means gain of electrons GER Gain Electrons Reduction Reduction Half Reactions show how Nonmetals or Cations gain electrons Balance charge Add 1+ 0 electrons to most positive side Ag + + 1e - Ag cation atom Reduction- electrons are on the left

13 Reduction means gain of electrons atom GER Gain Electrons Reduction Reduction Half Reactions show how Nonmetals or Cations gain electrons Balance charge Add 0 electrons to most 3- positive side N 2 + 6e - 2N 3- anion Reduction- electrons are on the left

14 That s REDOX Baby! JUST REMEMBER THIS LITTLE DITTY: LEO the lion says GER! LEO: Losing Electrons = Oxidation. GER: Gaining Electrons = Reduction

15 Let s Investigate 2Ag + + Cu 2Ag + Cu 2+ NET 2Ag + Cu Cu + + 2e - + 2e - 2Ag LEO GER

16 Ie) Real Estate Agents HELP OTHERS find real estate. Oxidizing and Reducing Agents Agents always HELP ANOTHER PARTY.

17 Oxidizing Agents cause oxidation by undergoing reduction. They gain electrons. Nonmetals and cations are oxidizing agents because they gain electrons. Cl 2 + 2e - 2Cl - Both can gain electrons Ca e - Ca

18 Reducing Agents cause reduction by undergoing oxidation. They lose electrons. Metals and anions are reducing agents because they lose electrons. 2N 3- N 2 + 6e - Al Al e - Both can lose electrons

19 Ox Agent Red Agent Oxidation Losing electrons 2Ag + + Cu 2Ag + Cu 2+ Gaining electrons Reduction

20 Meeting of retired CPR foremen at the Calgary Stampede in 1937.

21 CRAIGALLACHIE

22 The Thermite Reaction 2Al (s) + Fe 2 O 3(s) Al 2 O 3(l) + 2Fe (l) The reaction will reach a temperature of about 3000 C, meaning both reaction products are molten (mp Fe = 1530 C; mp Al 2 O 3 = 2030 C). This reaction fits the old definition of reduction that is, reducing the volume of a metal ore (Fe 2 O 3 ) to a smaller volume (Fe (s) ). This definition has been modified for the present day!

23 The Thermite Reaction NET Al (s) + Fe 3+ (s) Al3+ (l) + Fe (l) LEO GER