FUEL CELLS—ENERGY FOR A POWER-HUNGRY WORLD - Chemistry: Notable Research and Discoveries - page 136

But Earth and its resources are not boundless. Gasoline is made
from petroleum—oil pumped out of the ground. (Gasoline should not
be confused with natural gas, which is mostly methane and is burned
to heat homes, make electricity in generators, and for other purposes.)
Th e planet does not have an infi nite supply, and although no one is sure
how long the supply of petroleum might last, high consumption rates
may exhaust this resource within 50-100 years.
The left half of this electrochemical cell, containing a zinc electrode and zinc
sulfate solution, engages in an oxidation reaction. This reaction liberates
electrons and turns zinc atoms into zinc ions (Zn 2+ , which is a zinc atom
that has lost two electrons and therefore has a net positive charge of 2).
The zinc atoms come from the electrode, which is gradually depleted; the
zinc ions that are produced in the reaction enter the solution. In the right
half of the cell, a reduction reaction occurs; electrons combine with copper
ions to produce neutral atoms of copper. Copper ions leave the solution
in the process and collect at the copper electrode. Over time, the zinc
electrode and copper solution will run out of material, causing the reaction
to cease unless the material is replenished.