Nib asked
How does a battery cell work?
A battery stores no electricity. It stores chemicals that want to swap electrons, and it forces that swap to happen through your wire. The electrons in the wire were already there; the reaction just pushes them around the loop.
6 steps, drawn by Nib. Read it here, or watch him draw it. Updated .
1the myth
Most people picture a battery as a little tank of electricity that slowly empties. It is not. Inside are chemicals that can react and release electrons, and the battery makes that reaction happen in a way that pushes electrons through whatever you connect to it.
A battery stores chemical energy, not electricity.
a common mix-upA battery is not a tank of electrons. The wire and the metal already hold plenty of electrons; the chemical reaction pushes them around the loop.
2the hill
In the zinc and copper pair, zinc atoms give up electrons much more readily than copper does. Think of electrons sitting on a high shelf in zinc and a low shelf in copper. The drop between the shelves is the voltage, 1.10 volts for this pair. Electrons would roll down if they had a path.
Voltage is the drop in how much an electron wants to be where it is: zinc high, copper low, 1.10 volts.
Where do electrons want to travel in a zinc and copper cell?
Show the answer
From the zinc to the copper, down the hill.
3two halves
The cell has two halves. On the left a strip of zinc sits in a zinc sulfate solution. On the right a strip of copper sits in copper sulfate solution. Keeping them in separate beakers stops the electrons from jumping straight from zinc to copper ions, so they have to take the long way round, through a wire.
Two half cells, kept apart, force the electrons to travel through a wire.
4zinc gives
At the zinc strip, zinc atoms lose two electrons each and dive into the solution as zinc ions, written Zn becomes Zn two plus plus two electrons. This is oxidation, and the zinc is the negative end, the anode. The freed electrons cannot swim through the liquid to the other beaker, so the only path is the external wire.
Zinc is oxidised: Zn becomes Zn2+ plus 2 electrons, and the electrons leave through the wire.
5copper takes
At the copper strip, copper ions from the solution pick up the arriving electrons and settle on the strip as solid copper, Cu two plus plus two electrons becomes Cu. This is reduction and it makes the copper the positive end, the cathode. Without the salt bridge, the left beaker would pile up positive charge and the right beaker would run short, and the flow would stall in moments. Ions, not electrons, carry the current through the liquid.
Electrons go through the wire; ions carry the current through the liquid, closing the loop.
Do electrons travel through the salt bridge?
Show the answer
No. Ions move there; electrons only travel through the wire.
6the whole cell
The whole cell on one page: a metal that gives up electrons, a metal that takes them, a wire for the electrons to travel, and ions crossing inside to balance the charge. A battery goes flat when its reactants are used up, so the hill is gone. A rechargeable cell runs the reaction backwards with a charger. An alkaline AA uses zinc and manganese dioxide to make about 1.5 volts.
Zinc gives up electrons, they travel the wire to the other metal, ions balance the charge inside; when the zinc is gone the cell is dead.
Next time a remote dies, remember: nothing leaked out. The chemistry just ran out of road.