REDOX & Electrochemistry - LSU Chemistry
REDOX 18Voltage (or potential) represents the driving forcefor “pushing” the electrons from one location toanother (for example, from a reducing agent to anoxidizing agent). The higher the voltage the morestrongly the electrons will be pushed through thewire (or solution).A positive cell potential (voltage) indicates aspontaneous electrochemical reaction. A negativecell potential (voltage) indicates a non-spontaneousreaction (the opposite reaction will, therefore, bespontaneous!). Note that the sign notation here isopposite that we learned for ΔG!Problems: Which of the following substances is thebest reducing agent?a) Cu b) Zn c) Pb d) Ag e) H 2Which of the following substances is the bestoxidizing agent?a) Cu + b) O 3 c) O 2 d) Na + e) Li +
REDOX 19To calculate the voltage of an electrochemical cellone can simply add together the two half-cellreactions that make up the overall galvanic(electrochemical) cell.Let’s calculate the spontaneous cell potential(voltage) for our Cu/Zn cell. First look up the twohalf cell reactions from the table of StandardReduction Potentials:Cu 2+ (aq) + 2e - Cu(s) +0.34Zn 2+ (aq) + 2e - Zn(s) -0.76The more positive potential (relative to thehydrogen electrode) for the Cu 2+ reductioncompared to the Zn 2+ reduction means that Cu 2+ isa stronger oxidizing agent (wants to be reducedmore) than Zn 2+ .