Exploring Electrochemical Cells

 Redox reactions sometimes involve direct electron transfer, in which one substance immediately picks up the electrons another has lost. For instance, if you put a piece of zinc metal into a copper(II) sulfate solution, zinc gives up two electrons (becomes oxidized) to the Cu²⁺ ion that accepts the electrons (reducing it to copper metal). The copper metal begins spontaneously plating out on the surface of the zinc. The equation for the reaction is

Zn(s) + Cu²⁺ → Zn²⁺ + Cu

But if you separate those two half-reactions so that when the zinc is oxidized, the electrons it releases are forced to travel through a wire to get to the Cu²⁺, you get something useful: a galvanic or voltaic cell, a redox reaction that produces electricity.

In this section, I show you how that Zn/Cu²⁺ reaction may be separated out so that you have an indirect electron transfer and can produce some useable electricity. I also show you how electrolytic cells do the reverse, using electricity to cause a redox reaction. Finally, you see how rechargeable batteries both generate electricity and cause chemical reactions