Chemistry That Does Work
Electrochemistry & Batteries
14 minStudent plan
Where the voltage in a cell actually comes from, and why a battery sags under load and dies in the cold.
After this lesson you can
- Say which electrode oxidises and which reduces
- Explain where a cell's voltage comes from
- Explain why a battery sags under load
Oxidation, reduction and electron flow
Oxidation is loss of electrons; reduction is gain. They always happen together, since electrons have to go somewhere.
A battery separates the two halves so the electrons have to travel through an external circuit to get from one to the other. That flow is your current, and the chemistry is what pushes it.
At the negative electrode a material is oxidised, releasing electrons. At the positive electrode another material is reduced, consuming them. Ions move through the electrolyte inside the cell to keep charge balanced, and that internal ionic path is just as essential as the wire, which is why a dried-out electrolyte kills a cell as effectively as a broken lead.
In the full lesson
- Oxidation, reduction and electron flow
- Where the voltage comes from
- Internal resistance and temperature
This lesson comes with the Student plan. The first module of Chemistry is free.