1 / 18

Redox Reactions & Electrochemical Cells

Redox Reactions & Electrochemical Cells. I. Balancing Redox Reactions. I. Balancing Redox Reactions. STEP 1. Split Reaction into 2 Half-Reactions STEP 2. Balance Elements Other than H & O STEP 3. Balance O by Inserting H 2 O into eqns. as necessary

bryant
Download Presentation

Redox Reactions & Electrochemical Cells

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Redox Reactions & Electrochemical Cells I. Balancing Redox Reactions

  2. I.Balancing Redox Reactions • STEP 1. Split Reaction into 2 Half-Reactions • STEP 2. Balance Elements Other than H & O • STEP 3. Balance O by Inserting H2O into eqns. as necessary • STEP 4. Balance H with H+ or H2O (see 4a, 4b) • STEP 5. Balance Charge by Inserting Electrons as needed • STEP 6. Multiply Each 1/2 Reaction by Factor needed to make no. of Electrons in each 1/2 Reaction Equal • STEP 7. Add Eqns. & Cancel Out Duplicate terms, where possible

  3. I.Balancing Redox Reactions (continued) • STEP 4a. In ACID: Balance H by Inserting H+, as needed • STEP 4b. In BASE: Balance H by (i) inserting 1 H2O for each missing H & (ii) inserting same no. of OH- on OTHER SIDE OF REACTION as H2Os added in (i)

  4. I.Balancing Redox Reactions (continued) • Example • Complete and Balance Following Reaction: • CuS (s) + NO3 -(aq) Cu2+(aq) + SO42-(aq) • + NO (g) • STEP1. Split into 2 Half-Reactions • a.1 CuS Cu2+ + SO42- • b.1 NO3 - NO

  5. I.Balancing Redox Reactions (continued) • STEP 2. Balance Elements Other than H & O • Already O.K. !

  6. I.Balancing Redox Reactions (continued) • STEP 3. Balance O by inserting H2O into equations as necessary • a.3 CuS + 4H2O Cu2+ + SO42- • b.3 NO3- NO + 2H2O

  7. I.Balancing Redox Reactions (continued) • STEP 4. ACIDIC, so Balance H by inserting H+ as needed • a4. CuS + 4H2O Cu2+ + SO42- + 8H+ • b4. NO3- + 4H+ NO + 2H2O

  8. I.Balancing Redox Reactions (continued) • STEP 5. Balance Charge by inserting Electrons, where necessary • a5. CuS + 4H2O Cu2+ + SO42- + 8H+ + 8e- • b5. NO3- + 4H+ + 3e- NO + 2H2O

  9. I.Balancing Redox Reactions (continued) • STEP 6. Multiply each Eqn. by factor to make No. of Electrons in Each 1/2 Reaction the Same • a6. Multiply by 3x • 3CuS + 12H2O 3Cu2+ + 3SO42- + 24H+ + 24e- • b6.Multiply by 8x • 8NO3- + 32H+ + 24e- 8NO + 16H+ + 24e-

  10. I.Balancing Redox Reactions (continued) • STEP 7. Add Eqns. and Cancel Out Duplicated Terms • (a7 + b7) 8H+ • 3CuS + 12H2O + 8NO3- + 32H+ + 24 e- • 3Cu2+ + 3SO42- + 24H+ + 8NO +16 H2O +24e- 4H2O

  11. I.Balancing Redox Reactions (continued) So, the final, balanced reaction is: 3CuS(s) + 8 NO3-(aq)+ 8H+(aq) 3Cu2+(aq) + 3 SO42-(aq) + 8NO(g) + + 4H2 O(l)

  12. Checking mass balance and charge balance in Equation • L.H.S • 3 x Cu • 3 x S • 8 x N • 24 x O • 8 x H • (8 x 1-) + (8 x H+) = 0 • R.H.S. • 3 x Cu • 3 x S • 8 x N • 24 x O • 8 x H • (3 x 2+ )+(3 x 2- ) = 0

  13. Redox Reactions in Electrochemistry • Two Types of Electrochemical Cells: • 1. Galvanic • 2. Electrolytic • Galvanic Cell - Converts a Chemical Potential Energy into an Electrical Potential to Perform Work • Electrolytic Cell- Uses Electrical Energy to Force a Chemical Reaction to happen that would not otherwise occur

  14. Anode and Cathode in Electrochemistry • ANODE - Where OXIDATION takes place • (-e-) • CATHODE - Where REDUCTION takes place (+e-)

  15. Electrochemistry and the Metals Industry • Many Electrochemical Processes are used Commercially for Production of Pure Metals: • e.g. Al Manufacture (by electrolysis of Al2O3) • Mg Manufacture (by electrolysis of MgCl2) • Na Manufacture (by electrolysis of NaCl)

  16. Electrolylitic Production of Al using the HALL CELL (major plant in ALCOA, TN • Al2O3 dissolved in molten cryolite (Na3AlF6) at 950 0C (vs. 2050 0C for pure Al2O3) Graphite Anodes (+) C lining (Cathode) (-) Steel case Al Al2O3 in molten Na3AlF6 Al Molten Al

  17. Hall Cell for Al Manufacture

  18. Hall Cell Process Reaction: 2 Al2O3(sln) + 3C (s) 4 Al (l) + 3CO2 (g) Location of Hall cell plant in E. Tennessee through availability of inexpensive Hydroelectric power. Process uses 50,000 – 100,000 A.

More Related