What is a chemical cell?
A chemical cell works in the opposite way to an electrolytic cell: it changes chemical energy into electrical energy. It is the basis of every battery, from the dry cell in a torch to the accumulator in a car. A simple chemical cell needs two different metals dipped into an electrolyte and joined by a wire.
Key idea
The more electropositive metal (higher in the electrochemical series) becomes the negative terminal. It is oxidised and releases electrons that flow through the wire to the other metal.
How current is produced
The two metals have different tendencies to release electrons. The more reactive metal loses electrons more easily, so it becomes the negative terminal. Electrons then flow through the external wire from the negative terminal to the positive terminal, producing an electric current.
- The metal that is more electropositive is oxidised (negative terminal).
- The metal that is less electropositive is the positive terminal.
- The larger the difference between the two metals in the electrochemical series, the higher the voltage produced.
Example
In a zinc-copper cell, zinc is more electropositive, so zinc is the negative terminal. Electrons flow from the zinc to the copper through the wire. A magnesium-copper cell gives a higher voltage than a zinc-copper cell because magnesium and copper are further apart in the series.
Everyday chemical cells
The dry cell powers torches and remote controls and cannot be recharged. The lead-acid accumulator in cars can be recharged and reused, storing chemical energy again after use, which makes it far more economical over its lifetime. Modern phones and electric vehicles use rechargeable lithium cells that work on the same basic idea of turning chemical energy into electrical energy.
Remember
Two identical metals will not produce a voltage — the two electrodes must be different for a chemical cell to work.