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Oxidation and Reduction Reactions and Electrochemistry

Oxidation and Reduction Reactions and Electrochemistry

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Oxidation and Reduction Reactions and Electrochemistry

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  1. Oxidation and Reduction Reactions and Electrochemistry “The Ubiquitous Electron”

  2. Redox and Iron in your Body

  3. Types of Reactions • Ions or molecules react w/ no apparent change in electronic structure (ex. Double displacement) • Ions or atoms undergo changes of electronic structure, the way e- transfer or the way atoms share e- changes.

  4. Oxidation- Reduction Reaction Definition: • Chemical change that occurs when electrons are transferred between reactants • All oxidation reactions are accompanied by reduction reactions • Important: in the corrosion of metals, sources of energy, life processes

  5. Oxidation • Part of the redox rxn in which electrons are removed or apparently removed from an atom (loss of electrons  atom gets more positively charged)

  6. Movie

  7. Reduction • Part of the redox rxn in which electrons are added or apparently added to an atom (gain of electrons atoms get more negatively charged)

  8. Movie

  9. OIL RIG • Oxidation Is Losing • Reduction Is Gaining

  10. LEO the lion goes GER • Loss of Electrons in Oxidation • Gain of Electrons in Reduction

  11. Ionization or Solvation = the process of surrounding solute particles with solvent particles to form a solution Video “like dissolves like”

  12. Net Ionic Equations • When reactions take place in water chemists write the equation in ionic form (particles ionize – break into their ions in water) • Chemists only write down the ions that take part in the reaction • Spectator ions- ions that aren’t involved in the reaction (chemists don’t write these) • Makes rxn easier to balance

  13. Cu + NO3-1 Cu+2 + NO

  14. Show chemistry connections video: 7:36 minutes into video, found in redox folder

  15. Rules for Assigning Oxidation Numbers: • Use oxidation numbers (charges on atoms) to determine which atom underwent reduction and which atom underwent oxidation

  16. Rules: • The oxidation number for any free element is 0 (zero). Also any diatomic molecule is 0 (zero) H2, O2, I2, Cl2, F2, N2, Br2 Fe = 0 charge O2 = 0 charge

  17. The oxidation number of any monoatomic ion is equal to the charge written on the ion. Na +1 = +1 Cl-1 = -1

  18. Oxidation number of hydrogen in most of its compounds is +1 (except for LiH then H is –1) +1 Ex. HCl

  19. Oxidation # of oxygen in most of its compounds is –2.(except peroxides= -1) -2 Ex. H2O -1 Ex. H2O2

  20. Sum of the oxidation numbers of all of the atoms must equal the apparent charge of that particle.

  21. Ex. H2SO4 -zero charge +1 ? -2 H2SO4 +2 +6-8=0 S= +6

  22. Ex. NO3–1 ? + -2(3) = -1 +5 + (-6) = -1 N= +5

  23. Group 1 +1 Group 2  +2 Aluminum & Boron  +3 Group 17  -1

  24. Ex. KMnO4 K= Mn = O = +1 +7 -2

  25. Page 174 #67, 69

  26. Identifying redox, chemistry connections 11:29 minutes in

  27. Identifying Redox Reactions • First, figure out the oxidation numbers of all elements in the reaction • If oxidation number changes as you move from reactants to products it is REDOX.

  28. This is REDOX, Mg- loss e- (oxidation), H –gained e-(reduction) This is NOT REDOX

  29. P 618 in modern chem- #2, 15

  30. Oxidizing & Reducing Agents • Think of these agents as “causers” of redox rxns • Look at reactants • Some substances are better oxidizing or reducing agents

  31. Reducing Agents: substance that donates the electron (contains the atoms that are oxidized- or loss the e-) • Causes the reduction to occur • Oxidizing Agent: substance that gains the e- (contains the atoms that are reduced or gains e-) • Causes oxidation to occur

  32. Ex. 4Al + 3O2 2Al2O3 0 0 +3 -2 Al- lost e- , oxidized -reducing agent O- gained e-, reduced -O2 is the oxidizing agent

  33. Balancing Redox Reactions --Half Reaction Method • Half Reaction: equation that shows just the oxidation or reduction part of the rxn. • In balancing we balance each of the half rxns first, then add them together & reduce

  34. Steps: • Place oxidation #’s on everything after it is in the net ionic form. • ID the oxidation ½ rxn and the reduction ½ rxn • Write out the ½ rxns. • Balance the atoms by placing coefficients in front of the atoms  except for H and O Ex. Cl2 Cl-1 become Cl2  2Cl-

  35. 5. Place the # of electrons lost on the product side of oxidation ½ rxn, place # of electrons gained on reactant side of reduction ½ rxn 6. To balance hydrogens and oxygens: Acidic soln: add H+ & H2O Basic soln: add OH- & H2O

  36. Balance the charges (# e- lost must equal # e- gained) by using a least common multiple ( multiply the whole ½ rxn) • Add two ½ rxns together and reduce if necessary.

  37. Chemistry connections- balancing with blood alcohol tests (21:00-26:00)

  38. Electrochemistry Movie

  39. Because redox reactions involve electron transfer, the release or absorption of energy can occur in the form of electrical energy rather than heat • Electrochemistry is the branch of chemistry that deals w/ electricity related applications of redox reactions

  40. Electrochemical Process • Conversion of chemical to electrical energy • Ex. Flashlight batteries, biological systems, electroplating • If the substance that is oxidized is separated from the substance that is reduced you get an energy transfer of electrical energy instead of heat

  41. Electrons can be transferred from one side to the other through a connecting wire • Electric current moves in a circuit (while the electrons are being balanced by the movement of ions in solution)

  42. Part of a Cell: • Electrodes: • Conductor in a circuit that carries electrons from one substance to another • Anodes: electrode where oxidation occurs, anions (-) are attracted to this when they are oxidized by losing electrons (the positive electrode) • Cathode: electrode where reduction occurs, cations (+) are attracted to this when they are reduced by gaining electrons (negative electrode)

  43. Salt Bridge: • Porous partition that separates the 2 half reactions • Contains a conducting solution that allows the passage of ions from one compartment to the other w/ out mixing the solutions in the half reactions