1. Fuel Cells and Batteries

2. Electric circuit = a closed path along which electrons that are powered by an energy source can flow. Voltaic cell = a source of energy that generates an electric current by chemical reactions involving two different metals or metal compounds separated by a solution that is a conductor.

3. Battery = a connection of one or more cells Electrode = a connection of two or more cells Electrolyte = a solution or paste that conducts charge Dry cell = a cell that contains an electrolyte that is a paste Wet cell = a cell that contains a liquid electrolyte

4. Primary cell = a cell that can be used only once Secondary cell = a cell that can be recharged Fuel cell = a cell that generates electricity through the chemical reactions of fuel that is stored outside the cell. Solar cell = a cell that converts sunlight into electrical energy

5. In a cell/battery, electricity comes from a chemical reaction chemical energy is converted to electrical energy. Cells/batteries need replaced as the chemicals are being used up in the reaction to supply electricity. Some cells/batteries are rechargeable, e.g. nicad cells (nickel-cadmium cells) and the lead-acid battery used in cars/vans/buses.

6. Dry Cells metal cap zinc case carbon rod (graphite) ammonium chloride The ammonium chloride in the cell is an example of an The purpose of the electrolyte is to electrolyte. complete the circuit.

7. Electricity can be produced by connecting different metals together (with an electrolyte) to form a cell. Different pairs of metals connected in a cell give different voltages. This enables us to construct an V electrochemical series Voltmeter. Two different metals. Electrolyte, e.g. sodium chloride solution.

8. Magnesium is higher in the electrochemical series than copper. Magnesium gives electrons to the copper ions. The copper ions gaining these electrons form copper atoms (forms a brown solid). The magnesium atoms lose electrons to form colourless ions which dissolve in the solution.

9. Ion-electron equations can be used to show the reaction Start with Mg atoms Mg 2+ +2e Mg Cu 2+ +2eCu End with Cu atoms Mg atoms lose electrons to form Mg ions Electrons given to Cu ions Cu ions gain electrons to form Cu atoms

10. Electricity can be produced by connecting two different metals in solutions of their metal ions. A Copper Zinc Copper sulphate solutionZinc chloride solution to the lower metal. Electrons flow in the wires from the metal high in the electrochemical series Ion bridge/salt bridge e-e- e-e-

11. The purpose of the “ion bridge” (“salt bridge”) is to complete the circuit. A Copper Zinc Copper sulphate solutionZinc chloride solution through the ion bridge/salt bridge.Ions flow through solutions and Ion bridge/salt bridge e-e- e-e- The movement of ions through the ion bridge completes the circuit.

12. Cells/batteries compared to mains electricity. Ease of transport: cells/batteries are highly portable / mains electricity is not! Safety: cell/battery voltages/currents are safer than those of mains electricity. Costs: cells/batteries are much more expensive. Uses of finite resources: making cells/batteries uses up more finite resources than producing mains electricity.