Electrochemistry

ElectrochemistryVoltaic Cells

Voltaic (Galvanic) Cells - spontaneous reaction used to produce electrical energy.

Salt Bridge Cells

Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)

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The salt bridge allows the current to flow but prevents contact between Zn and Cu2+, which would short-circuit the cell.salt bridge demo

For the reaction:Zn(s) + 2H+(aq) Zn2+(aq) + H2(g)use an inert Pt electrode for H+/H2 half-cell. Bubble in H2 over the Pt electrode.

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Standard VoltagesEo = cell voltage when all species are at standard concentrations (1 atm for gases, 1M for solutions).

Zn + 2 H+ Zn2+ + H2Eo = + 0.762 V = Eox (Zn) + Ered (H+)Ered of H+ is arbitrarily set to zero.

Appendix E on page 1117 is a list of standard reduction potentials. The oxidation potential is obtained by changing the sign.

Ex Find the cell potential of the Zn - Cu cell.

The more positive the value of Ered, the more easily reduced and the stronger the oxidizing agent.

The more negative the value of Ered, the more easily oxidized and the stronger the reducing agent.

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Calculation of Eo.Eo = Eox + Ered Cl2(g) + 2 Br-(aq) 2 Cl-(aq) + Br2(l)

Eo = Ered + Eox = ECl2 + EBr- = 1.360 V - 1.077 V= +0.283 VSince the calculated voltage is positive, this voltage can occur in a voltaic cell and the cell will produce electricity.

Ex - What, if anything, will happen when bromine is added to a solution of tin(II) chloride?

If Br2 is reduced, Sn2+ cannot beWill give a negative E with Br2

Notes Quizhttps://docs.google.com/spreadsheet/embeddedform?formkey=dHFNTkFGU1pPUEpyZ0pqNnktWGVkYVE6MQ