Cells around us
Besides the appliances that run on mains electricity, we use many that run on electrochemical cells and batteries: toy cars, torches, calculators, computers and mobile phones.
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The cells in those devices are small. The battery that starts a motor car is large — and it is not one cell but several electrochemical cells joined together.
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What a cell does
In an electrochemical cell the chemical energy stored in its compounds is turned into electrical energy.
Where this chapter starts
You met electrochemical cells in grade 10, as one use of the activity series: two different metals in an electrolyte give a current, and the more reactive metal is the one that dissolves. This chapter opens the cell up. We look at what happens at each metal, write it as equations, and give the two halves of the reaction their proper names — oxidation and reduction. Then we turn the idea round: instead of a reaction making a current, a current will make a reaction happen. That is electrolysis, and it is how sodium is made, how jewellery is gold-plated and how copper is purified. Last comes rusting, which turns out to be a tiny electrochemical cell at work on every iron nail.
A cell turns chemical energy into electrical energy
A battery is several electrochemical cells together. Each cell turns the chemical energy of its compounds into electrical energy.