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Primary and Secondary Cells

Primary and Secondary Cells. Outcome 10: Understand the process of charging and discharging cells. Definition . A primary cell is one in which the electrochemical reaction is not reversible.

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Primary and Secondary Cells

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  1. Primary and Secondary Cells Outcome 10: Understand the process of charging and discharging cells.

  2. Definition • A primary cell is one in which the electrochemical reaction is not reversible. • A secondary cell has cell chemistry that can be reversed with the application of a current in the opposite direction which is given in the discharge reaction.

  3. Electrolytic Cells • The redox reaction in a galvanic cell (battery) is spontaneous when the anode and cathode are joined by a conductor. • The redox reaction in an electrolytic cell is nonspontaneous. • Electrical energy is required to induce the electrolysis reaction.

  4. Electrolytic Cells • An example of an electrolytic cell is shown, in which molten NaCl is electrolyzed to form liquid sodium and chlorine gas. • Sodium ions move toward the cathode, where they are reduced to sodium metal. • Chloride ions migrate to the anode and are oxidised to form chlorine gas.

  5. Comparing Galvanic and Electrolytic Cells

  6. The definitions for anode and cathode remain the same. Oxidation occurs at the anode. Reduction occurs at the cathode.

  7. Why can some cells be recharged? The chemistry must be reversible. Applying a reverse current may cause other reactions, rather than the reformation of the initial reactants.

  8. Why can some cells be recharged? Some batteries release gases as they discharge which may not be available for the reverse reaction.

  9. Why can some cells be recharged? To be classed as rechargeable, the reverse process must be able to occur thousands of times.

  10. Why can some cells be recharged? The reverse reaction must return the reactants to the same physical state. Rough or filamentous growths on one or both electrodes may eventually cause the electrodes to touch and internally short out the battery.

  11. Further Reading SCIENTIFIC AMERICAN: How do rechargeable (that is, zinc-alkaline or nickel-cadmium) batteries work and what makes the reactions reversible in some batteries, but not in others? Click Here!

  12. Further Reading BATTERY UNIVERSITY Corrosion, Shedding and Internal Short Click Here!

  13. Homework • Please read the previous web pages and submit a set of draft summary notes of no more than one A4 page. • The draft summary must be hand written

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