A chemical cell produces a voltage from a chemical reaction. It is made of two different metals in an electrolyte. The bigger the difference in reactivity between the metals, the bigger the voltage. A battery is two or more cells joined in series. In non-rechargeable cells, the reaction stops when a reactant is used up; rechargeable cells can be reversed by applying an external current.
A hydrogen fuel cell is supplied with hydrogen and oxygen. Hydrogen is oxidised at one electrode and oxygen reduced at the other, giving a voltage, and the only product is water. Fuel cells are efficient, quiet and produce no carbon dioxide where they are used. However, hydrogen is a flammable gas that is hard to store, and it is often made using fossil fuels.
Worked example
Which pair of metals would give the bigger voltage: zinc–copper or iron–copper?
- Voltage depends on the difference in reactivity.
- Zinc is more reactive than iron, so zinc and copper are further apart.
Answer:Zinc–copper gives the bigger voltage.
Key words
- chemical cell
- produces a voltage from a reaction
- battery
- two or more cells in series
- fuel cell
- combines a fuel and oxygen to produce electricity
- rechargeable
- the reaction can be reversed by a current
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NGSS-referenced: HS-PS1-2