The Chemical Cell

  • A chemical cell is a source of electrical energy.
  • The simplest design consists of two electrodes made from metals of different reactivity immersed in an electrolyte and connected to an external voltmeter by wire, creating a complete circuit.
  • A common example is zinc and copper.
  • Zinc is the more reactive metal and forms ions more easily, readily releasing electrons.
  • The electrons give the more reactive electrode a negative charge and sets up a charge difference between the electrodes.
  • The electrons then flow around the circuit to the copper electrode which is now the more positive electrode.
  • The difference in the ability of the electrodes to release electrons causes a voltage to be produced.
  • The greater the difference in the metals reactivity then the greater the voltage produced.
  • The electrolyte used also affects the voltage as different ions react with the electrodes in different ways.

How reactivity affects voltage in electrochemical cells, IGCSE & GCSE Chemistry revision notes

Chemical cell made with Cu and Mg. These metals are further apart on the reactivity series than Cu and Zn and produce a greater voltage

Batteries

  • Chemical cells include the familiar batteries used in everyday appliances and cars.
  • Batteries work by connecting two or more cells in series, which combine to give a larger overall voltage.
  • Over time the electrodes degrade as the reactions that occur there are irreversible.
  • This happens as the ions in the electrolyte and the metal ions at the electrodes are converted into products.
  • Chemical cells produce a voltage only until one of the reactants is used up and when this occurs the battery dies or goes flat.
  • The products formed cannot be reverted back into reactants as the reaction is irreversible and the battery must be replaced.
  • This happens in non-rechargeable batteries such as alkaline batteries.
  • In rechargeable batteries the reactions are reversed by connecting the cells to an external electrical supply.
  • This recharges the battery which can then be used again.

AQA GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.