A voltaic cell converts chemical energy to electrical energy using two metals of different reactivity in an electrolyte; the more reactive metal is the negative terminal.
A voltaic cell converts chemical energy into electrical energy using two metals of different reactivity dipped in an electrolyte. The more reactive metal is the negative terminal. Malay: sel voltan · Chinese: 伏打电池.
A voltaic cell works because a spontaneous redox reaction is split between two electrodes. The more reactive metal loses electrons (it is oxidised) and becomes the negative terminal; those electrons flow through the external wire to the less reactive metal, giving a current that can light a bulb or move a galvanometer needle. The bigger the difference in reactivity between the two metals, the larger the voltage produced. This is the opposite energy change from electrolysis, which uses electricity to force a reaction.
Example. In a cell made of magnesium and copper in an electrolyte, magnesium is more reactive, so it is oxidised (Mg to Mg2+ plus 2e-) and forms the negative terminal. Electrons flow from the magnesium to the copper through the wire, and the reading on the voltmeter is higher than for a zinc and copper cell because magnesium and copper are further apart in the reactivity series.
Confusion to avoid. Do not muddle a voltaic cell with an electrolytic cell. A voltaic cell produces electricity from a spontaneous reaction, while an electrolytic cell consumes electricity to drive a non-spontaneous one, and the sign of each terminal is reversed between the two. Remember that in a voltaic cell the negative terminal is the more reactive metal.
Reading the voltmeter. The voltage of a voltaic cell is a rough measure of how far apart the two metals stand in the reactivity series, so a magnesium and copper pair gives a larger reading than a zinc and copper pair. If you replace one metal with a more reactive one, predict a higher voltage; if the two metals are close together in reactivity, predict a smaller one. This is a common way for a question to test whether you can apply the reactivity series.
Predicting the terminals. Use the reactivity series to decide which metal is oxidised and therefore negative, then write the two half-equations. This links the cell directly to displacement, where the same electron transfer happens without a wire, and it is a frequent structured task in SPM Chemistry.
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