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Electrochemistry

Electrochemistry. Electrochemistry. The study of the interchange of chemical and electrical energy Redox reactions OILRIG Oxidation – loses electrons Reduction – gains electrons. Galvanic Cells. Anode – electrode at which oxidation occurs Cathode – electrode at which reduction occurs

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Electrochemistry

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  1. Electrochemistry

  2. Electrochemistry • The study of the interchange of chemical and electrical energy • Redox reactions • OILRIG • Oxidation – loses electrons • Reduction – gains electrons

  3. Galvanic Cells • Anode – electrode at which oxidation occurs • Cathode – electrode at which reduction occurs • Electrons flow from anode to cathode • Salt bridge is necessary so no buildup of charge occurs • Goal of an electrochemical cell is to get cell voltage or emf (Ecell) • Electromotive force • Pushes the current through cell • Volt – unit of electrical potential

  4. Cell Notation • Zn(s) | Zn2+ (1M) || Cu2+ (1M) | Cu(s) Anode Salt Bridge Cathode • Written in order of electron flow • Standard conditions – 1 atm and 1M solution

  5. Measured voltage of a cell is determined by the half-reactions taking place • Half-reactions all have an electrode potential (E°) and by adding these together, we get the emf (voltage) of the cell = Ecell • All E° are referenced to a SHE (standard hydrogen electrode) • SHE E° = 0

  6. Example Zn(s)  Zn2+ + 2e-E° = 0.76 V 2e- + Cu2+ Cu(s) E° = 0.34 V Zn(s) + Cu2+  Zn2+ + Cu(s)E°cell = 1.10 V

  7. E° - What does it mean? • Positive E° indicates electrons flow as indicated • If negative, both half-reactions need to be reversed • Need one reduction/oxidation • +E°cell = spontaneous • -E°cell = not spontaneous • Reverse is spontaneous • For half-reactions – the more positive E° is, the more likely it is to happen and • The more negative E° is the more likely the reverse is to happen

  8. 17.1 Example • Consider a galvanic cell based on the reactionAl3+(aq) + Mg(s) Al(s) + Mg2+(aq) • Break apart into half reactions • Give the balanced cell reaction and calculate E°

  9. 17.2 Example • Describe completely (E°, balanced reaction, schematic diagram) the galvanic cell based on the following half-reactions under standard conditionsAg+e- AgFe3+ e- Fe2+

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