1. Electrochemical Cells
Lesson 8

2. Electrical Energy from Chemical Reactions
Just like water molecules in a waterfall have gravitational potential energy, the electrons in a battery have electrical potential energy.
Even if a battery is not connected to a circuit, the stationary electrons at the negative terminal have electric potential energy.
At the instant a battery is made, a chemical reaction occurs, and the stored energy is released by the reaction exerts a force on the electric charges and pushes a certain number of them to the terminals of the battery.

3. Electrons can be released with their electric potential energy in a circuit only when the switch is closed and electrons can flow completely around the circuit.

4. Primary Cells
There are two basic types of primary cells: the primary wet cell (voltaic cells) and the primary dry cell.
In a primary cell, chemical reactions use up some of the materials in the cell as electrons flow from it. When these materials have been used up, the cell is said to be discharged and cannot be recharged.

5. The Primary Wet Cell
The primary cell, or voltaic cell, was developed in 1800 by and Italian scientist, Alessandro Volt. It is called a wet cell because it is made of two pieces of metal that are placed in a liquid. The metal plates, which are usually zinc and copper, are called electrodes.

6. The Primary Wet Cell
The liquid in the cell is called the electrolyte. An electrolyte is any liquid that conducts an electric current. The zinc reacts with the electrolyte which releases electrons that collect on the zinc plate, which is called the negative electrode. At the same time, the positive charges collect on the copper plate, which is called the positive terminal of the cell. The electric charges collected remain static on each electrode. Cells discharge only when connected to a closed electric circuit.

7. Disadvantages Danger of spilling the corrosive electrolyte
The zinc and electrolyte must continually be replaced

8. The Primary Dry Cell
The dry cell functions in the same way as the wet cell but the electrolyte is a moist paste instead of a wet liquid. When most of the negative electrode has been used up, by the chemical reaction, the electrons stop flowing, and the cell is discharged.
Example: A alkaline battery

9. Secondary Cells
A secondary cell can be discharged and recharged hundreds of times.
It is called a secondary cell because it there are two chemical processes involved one to discharge the cell, and another to recharge it to its original state.

10. Building a Simple Wet Cell
Lab