Electrochemistry The batteries we use to power portable computers and other electronic devices all rely on redox reactions to generate an electric current. Redox reactions are central to the development of small, light, long-lasting power sources. To a large extent, the future development of technology depends on the capabilities of these power sources. In this chapter, we see what is involved in using chemical reactions to generate electricity.

lose electrons oxidize gain electrons reduced LEO goes GER lose electrons oxidize gain electrons reduced

Balance: in acid solution MnO4-(aq) + C2O42-(aq)  Mn2+(aq) + CO2(g)

anode oxidation and reduction at the cathode An Ox and a Red Cat anode oxidation and reduction at the cathode FAT CAT electrons travel from anode to cathode

Example 1: For the following write the balanced cell reaction, calculate Eocell and represent the cell using line notation : MnO4-(aq) + H+(aq) + ClO3-(aq)  ClO4-(aq) + Mn+2(aq) +H2O(l)

Example 2: Describe completely the galvanic cell based on the following half reactions under standard conditions. Ag+ + e-  Ag Fe+3 + e-  Fe+2

Example 3: Which of the following substances is the best reducing agent? a) Cu b) Zn c) Pb d) Ag e) H2 Which of the following substances is the best oxidizing agent? a) Cu+ b) O2 c) Na+ d) Li+

Example 4: Predict Eo and the direction of the redox reaction. 1. 2Al(s) + 3Sn+4(aq)  2Al+3(aq) + 3Sn+2(aq) 2. 2Br-(aq) + I2(s)  2I- (aq) + 3Sn+2(aq)

at equilibrium DG = 0 and Q = K ΔGo = -n FEo at equilibrium DG = 0 and Q = K

Example 5: Determine the cell potential at 25oC for Fe(s) + Cd+2(aq)  Fe+2(aq) + Cd(s) when [Fe+2] = 0.01 M and [Cd+2] = 1.0 M.

Example 6: For the redox reaction S4O6-2 (aq) + Cr+2(aq) Cr+3(aq) + S2O3-2(aq) Balance the equation and calculate Eo and K.

Example 7: Calculate ΔGo using the Eo for the reaction Cu+2(aq) +Fe(s)  Cu(s) + Fe+2(aq)

Example 8: Determine the direction of electron flow and designate the anode and cathode for a concentration cell constructed from solutions of 0.01 M Fe+2 and 0.10 M Fe+2.

coulomb = (amp) (sec) 1mole e- = 96,500 C

Example 9: A current of 1.5 amps is passed for 15 minutes in a solution containing cupric ions. What mass of copper is produced?

Example 10: How long will it take to plate out 1 gram of Ni from aqueous Ni+2 using a current of 20 amps?

Example 11: Write the half reactions that would result from a current passing through each of the following solutions. a. molten NaBr b. NaBr(aq) c. CuCl2(aq)

Example 12. Suppose a solution in an electrolytic cell contains Cu+2, Ag+, and Zn+2. Which ion will be reduced at the cathode at the lowest voltage?