1. Electrochemical Cells Ms. Petrauskas

2. Voltaic cells • Chemical reactions use up some of the materials in the cell as electrons flow from it • A battery is a connection of 1 or more cells • Primary wet (voltaic) • Primary dry

3. Volta’s Voltaic Cell • Developed 1800, by Alessandro Volta. • Wet, because made from two pieces of metal in a liquid • Metal terminals are usually zinc and copper; called electrodes • Liquid is an electrolyte, a fluid that conducts electricity

4. The Reaction • Takes place on the surface of the electrodes that is in contact with the electrolyte • Depends on the movement of electrons and ions

5. Dangers…. • Spilling the corrosive electrolyte • Continuous need to replace the zinc and copper

6. Wet cells • Liquid electrolyte • Mostly sulphuric acid (strong and inexpensive) • Volta cell is a wet cell

7. Primary dry cell • Work much the same as wet cells • Moist paste instead of liquid electrolyte • When most of the negative electrode has been used up, electrons stop flowing, the battery is dead

8. Types • Zinc (-ve)- carbon(+ve) (cheap, not very long lasting) • Alkaline (expensive, long lasting) • +ve manganese dioxide • -ve powdered zinc • Has a brass current collector • Button • Silver oxide or zinc air

9. Dangers… • Do not recharge disposable dry cell batteries, because it will cause them to heat up and the cell casing will break open or explode. • Overtime even an unused dry cell will gradually discharge. They can become dead without use • Disposal bad for the environment

10. Secondary cells • Can be discharged and then recharged • Secondary because two chemical processes involved • Discharge • Recharge • The recharge is a result of an electric current being passed in the opposite direction • Lead acid car battery is a secondary wet cell

11. Solar cells • Converts solar energy to electrical energy • Strikes semi-conductor, e- are knocked loose from atoms • E- move to create electricity

12. Why do batteries die? • Batteries die when the reactants get used up like when the zinc or sulfuric acid can no longer react. • Reactive forms change after reacting and are not easily reversed

13. Direct Current • Electrons move in one direction only!- From negative to positive • Was used to supply homes with electricity. • Still the type of electricity seen with batteries • Was found that a large amount of energy was lost this way.

14. Alternating Current • Alternating current is the flow of electrons that alternates direction in an electrical circuit • This is the type of electricity that NOW powers your home.

15. AC-how it works… The polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. Connected to a load, this reversing voltage polarity will create a reversing current direction in the circuit.

16. AC- Why is it better • Less electricity lost over distance • Simpler generator design • Range of current possible when transformers distribute.

17. What battery properties are best? • Golf cart • Flashlight • Portable drill • Key chain light • Pacemaker • Hearing aid • Computer