How do batteries provide electricity?
Batteries are a type of voltaic/electrochemical cell, in which chemical reactions within the battery encourage the flow of electrons, conducting an electric flow.
The relationship between the chemical reactions and electricity is called electrochemistry.
One type of voltaic/electrochemical cell is as followed:
Fig. 1: solid zinc (called an electrode) submerged in ZnSO4 solution as one compartment (or a half-cell), and solid copper electrode submerged in CuSO4 in the other half-cell, connected by a salt bridge and a wire.
As an electrical flow is generated through the transfer of electrons (notated by e-), one metal must transfer its electrons to the other through the wire.
This is called an oxidation-reduction reaction, where oxidation = loss of electrons, and reduction = gaining electrons. A good mnemonic device to remember this is LEO (the lion) goes GER.
The half-cell containing the oxidized metal is called the anode, and the latter is the cathode:
As copper has a higher electronegativity (attraction for electrons) than zinc, zinc will be oxidized, and copper will be reduced; the zinc electrode is the anode, and the copper electrode is the cathode.
How does the transfer of electrons work?
Refer to this graph of the zinc half-cell.
Due to the connection of the zinc and copper half-cells, solid zinc loses its tug-of-war of electrons to electronegative copper, letting go of 2 electrons (notated by a 2+) and losing its solid form, causing it to become dissolved in the solution:
The electron transfers through the wire, generating the electric flow. The electrons then go to the copper solid electrode.
There, the electrons attracts copper ions (Cu 2+, which needs to gain 2 electrons to become stable) in CuSO4 solution that consequently change from aqueous to solid:
From this process, the zinc solid will become smaller, and the copper much bigger:
Now that we know what generates the electric flow...
What is the significance of the salt bridge?
The salt bridge transfers negative ions into the zinc compartment to balance the charges.
Vise versa; when copper ions in the CuSO4 gains electrons and become a stable solid, negatively charged SO4 ions create a more negative charge in the copper half-cell:
From this information, our big picture mechanism depicts a cycle of charges that conducts an electrical flow for things such as batteries.
It should be known that this zinc and copper exchange is only one example of electrochemical cells. For more information and examples, check out this website.
References:
1.) Voltaic Cells. ChemPages Netorials, www2.chem.wisc.edu/deptfiles/genchem/netorial/rottosen/tutorial/modules/electrochemistry/03voltaic_cells/18_31.htm.
2.) DeWitt, Tyler. "Galvanic Cells (Voltaic Cells)." Youtube, 14, Aug. 2015,https://www.youtube.com/watch?v=7b34XYgADlM.
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